Line large baking sheet with parchment or silicone liner. In a small dish, combine seasonings: 1/2 tsp cumin, 1/2 tsp cayenne pepper, 1 tsp salt and 1/4 tsp black pepper and evenly sprinkle seasoning mix over both sides of tilapia.
Lightly drizzle fish with olive oil and dot each piece with butter. Bake at 375 for 20-25 min. To brown edges, broil for 3-5 minutes at the end if desired.
Combine all Taco sauce ingredients in a medium bowl and whisk until well blended.