Summer Halibut and Delicata Squash Frittata

Here’s the honest pitch: this is a frittata you can build almost entirely from what’s already sitting in your fridge on a summer weeknight, and it turns leftover halibut into something that doesn’t taste like leftovers. If you’ve got a piece of cooked fish you don’t know what to do with and a delicata squash going soft in the drawer, this is the dish that uses both without asking much of you.

Summer halibut and delicata squash frittata isn’t fussy. It’s eggs, a mild, flaky fish, and squash that doesn’t need peeling, baked together until the top just sets and the edges pull slightly away from the pan. Ten minutes of hands-on work, thirty total, and it works hot, room temperature, or cold out of the fridge the next morning.

Why This Recipe Is Worth Making

The practical case first: it’s one pan, one oven pass, and it stretches a small amount of fish across a full meal for four people. Halibut isn’t cheap, and this is a smart way to make four ounces do the work of a pound.

The other case is that it’s genuinely flexible about timing. You can bake it right before dinner, or make it in the morning and eat it cold for lunch, and neither version suffers. Delicata squash is also one of the few winter squashes with skin thin enough to eat, which means no peeling — a real time-saver on a weeknight when you’re not trying to fight with a vegetable peeler and a hard squash.

What You’ll Need

Serves 4.

• 8 large eggs
• 1/4 cup whole milk (or half-and-half for a richer texture)
• 1/2 teaspoon salt, plus more to taste
• 1/4 teaspoon black pepper
• 8 ounces cooked halibut, flaked into large pieces (leftover grilled or baked halibut works well; poached also works if that’s what you have)
• 1 small delicata squash (about 12 oz), halved, seeded, and sliced into thin half-moons — no need to peel
• 2 tablespoons olive oil, divided
• 1/2 small yellow onion, thinly sliced
• 2 cloves garlic, minced
• 1/3 cup grated Parmesan, plus more for the top
• 2 tablespoons fresh chives or dill, chopped
• Zest of 1/2 lemon

No halibut on hand? Any firm white fish works — cod, sea bass, or even canned tuna in a pinch, though canned tuna will bring a stronger, saltier flavor, so cut back on the added salt if you go that route.

How to Make It

1. Preheat the oven to 375°F. Get this going first so it’s ready by the time your stovetop work is done.
2. Cook the squash. Heat 1 tablespoon olive oil in a 10-inch oven-safe skillet (cast iron works great here) over medium heat. Add the delicata squash slices in a single layer and cook for 6 to 7 minutes, flipping once, until they’re golden at the edges and tender enough to pierce easily with a fork. Don’t rush this step — undercooked squash stays firm and starchy in the finished frittata, which is a texture nobody wants to bite into.
3. Add the onion and garlic. Push the squash to one side, add the remaining olive oil, then the onion. Cook for 3 to 4 minutes until it softens and turns translucent, then stir in the garlic for the last 30 seconds, just until it smells fragrant — garlic burns fast, so keep an eye on it and keep the pan moving.
4. Whisk the eggs. While the vegetables cook, whisk the eggs, milk, salt, and pepper together in a bowl until fully combined and slightly frothy on top. This is also when you fold in the Parmesan.
5. Add the fish and combine. Scatter the flaked halibut evenly over the squash and onion in the skillet. Pour the egg mixture over everything, giving the pan a gentle shake so the eggs settle evenly around the fish and vegetables.
6. Set the edges on the stovetop. Let the pan sit undisturbed over medium-low heat for 2 to 3 minutes, just until you see the outer edge of the eggs start to firm up and pull slightly from the sides of the pan. This head start means less time in the oven and a better texture overall.
7. Finish in the oven. Transfer the skillet to the oven and bake for 12 to 15 minutes, until the center is just set — it should look barely wobbly, not liquid, when you give the pan a gentle nudge. A frittata keeps cooking a little from residual heat once it’s out, so don’t wait for it to look fully firm in the oven or you’ll overshoot into rubbery territory.
8. Rest, then finish. Let the frittata rest in the pan for 5 minutes before slicing. Scatter the chives or dill and lemon zest over the top just before serving — adding them any earlier means the heat dulls their color and brightness.

Tips That Actually Make a Difference

Use a pan you trust in the oven. A nonstick skillet with a plastic handle has no business going into a 375°F oven, and cast iron or stainless steel with a metal handle is what you actually want here.

Don’t skip searing the squash before the eggs go in. Squash added raw to the egg mixture won’t cook through fully in the short bake time, and you’ll end up with pale, underdone pieces instead of the golden, slightly caramelized ones that make this frittata worth eating.

If your halibut is cold from the fridge, let it sit out for 10 minutes before flaking it into the pan. Ice-cold fish dropped into warm eggs cools the whole mixture down and slows the set, which throws off your timing.

Mistakes to Watch Out For

The biggest one: overbaking. A frittata left in the oven “just to be safe” turns rubbery and squeaky against your fork — eggs don’t forgive extra time the way a casserole does. Pull it when the center still has a slight jiggle.

Second: skipping the stovetop head start. Going straight into the oven with raw egg mixture means the bottom overcooks by the time the center sets, giving you a tough, browned bottom layer under a barely-set top.

Third: overcrowding the fish. If you use a full pound of halibut instead of the 8 ounces called for, you’ll end up with more fish than egg can properly bind, and the frittata will fall apart when you slice it instead of holding together in clean wedges.

Easy Ways to Change It Up

Swap the delicata for zucchini in peak summer — cook it the same way, though it releases more water, so give it an extra minute or two to dry out in the pan before adding the eggs. For a dairy-free version, skip the Parmesan and milk, and use a splash of unsweetened oat milk instead — the texture will be slightly less rich, but it still sets properly. If you want more vegetables in the mix, a handful of chopped spinach stirred in with the garlic wilts down fast and adds color without changing the timing.

What to Serve It With

A simple green salad with a sharp vinaigrette is really all this needs — the acidity cuts through the richness of the eggs and cheese. For a heartier dinner, add crusty bread or roasted potatoes on the side. This also works well for a weekend brunch spread alongside fresh fruit, since it holds its shape and temperature well sitting out on a table.

Leftovers and Reheating

Store leftover frittata in an airtight container in the refrigerator for up to 3 days. It’s genuinely good cold, straight from the fridge, which makes it an easy grab-and-go breakfast. If you want it warm, reheat individual slices in a 325°F oven for about 8 minutes, or in a dry skillet over low heat, covered, for 4 to 5 minutes. Skip the microwave if you can — it tends to make the eggs rubbery and can dry out the fish.

Approximate Nutrition Per Serving

Values are approximate estimates based on standard ingredient data and are provided for general informational purposes only. Actual nutrition will vary based on specific brands and portion sizes used.

Final Thoughts

This is the kind of recipe worth keeping in rotation specifically because it doesn’t demand a grocery run — it’s built to use up what you already have without tasting like a compromise. Make it once with whatever fish and squash are in your kitchen this week, and you’ll have a template you can lean on for months.