Heat the oven. Put a rack in the middle and heat the oven to 220°C (425°F). Use a large rimmed sheet pan, or two.
Prep the kohlrabi (about 12 minutes). Cut off the stems and roots, peel the bulbs, and cut them into 1/2-inch (1.3 cm) pieces. Toss them with 1 tbsp (15 ml) of the oil, the salt, and the pepper, and spread them in a single layer.
Start roasting (15 minutes). Roast the kohlrabi alone, stirring once halfway. The edges should begin to turn pale gold.
Prep the rest. While the kohlrabi roasts, toss the chorizo, tomatoes, zucchini, onion, and garlic with the remaining 1 tbsp (15 ml) of oil.
Add everything and roast (15 to 20 minutes). Scatter the second batch over the kohlrabi, mix gently, and return the pan to the oven. Roast until the chorizo coins are browned and crisp at the edges, the tomatoes have burst, and the kohlrabi is tender in the center and golden at the edges. Stir once halfway. The pan will smell smoky and sweet, and the oil in the bottom will be paprika red.
Finish. Squeeze the lemon over the pan, scatter the parsley, and taste. Add a pinch of salt only if you need it.
Serve. Spoon the vegetables and chorizo onto plates and drizzle the red pan oil over the top. Lemon wedges go on the side.