Preheat oven to 400 degrees. On a baking sheet, toss onions and peppers in avocado oil, spread out evenly on the baking sheet but leave room for the fish.
In a small bowl, combine cumin, chili powder, garlic powder, brown sugar & salt. On a large plate, pat the fish dry and rub with cumin mixture.
Place the fish on the baking sheet. Bake for 15-20 minutes or until fish is cooked through to 145 degrees. Cooking time will vary & depend on the size & thickness of your fish.
In the meantime, combine yogurt, mayo, lime juice, sriracha & salt to make a sauce. Add slaw mix to a bowl & mix in ranch dressing. Assemble tacos with fish, veggies, slaw, avocado, cilantro & whatever else you want.