Preheat oven to 400° + line a sheet pan with foil; cut onion into thin slices, add fish + onions to pan + drizzle with 2 tbsp oil, salt/pep + fave seasonings; bake 8-12 min until firm, opaque + cooked through; using a fork, flake fish into bite-size pieces, mix with 4 tbsp sauce + salt/pep

Lightly oil a small baking dish; divide fish + onions among 4 tortillas + roll up; place tortillas seam side down in baking dish + top with 4 tbsp sauce

Cover dish with foil + bake 10 min; remove foil, sprinkle on ½ cup cheese + bake 10 min until cheese is hot + bubbling