In a small bowl, whisk the mayonnaise, lemon juice, and a pinch of salt. Toss with the shredded cabbage and set aside.
Pour the apple cider into a small saucepan and bring to a simmer over medium heat. Cook, stirring occasionally, until reduced by about half and thick enough to coat the back of a spoon, 8 to 10 minutes.
Whisk in the apple cider vinegar and Dijon mustard, then remove from heat and swirl in the butter until glossy. Set aside.
Pat the tilapia fillets dry and season both sides with salt and pepper.
Heat the olive oil in a skillet over medium-high heat. Add the tilapia and cook for 3 minutes per side, until golden and the fish flakes easily with a fork.
Brush each fillet with about 1 tablespoon of the cider glaze while still warm.
Warm the tortillas briefly in a dry skillet or the microwave until pliable.
Layer the cabbage slaw and apple slices down the center of each tortilla, then top with a glazed tilapia fillet.
Fold in the sides of the tortilla and roll tightly from the bottom up.
Slice in half and serve immediately.