Thaw the fish for a couple of hours. Unseal the packet and pat dry the fish using a kitchen towel to get the moisture out.
In a small bowl, mix taco seasoning, cumin powder, cayenne pepper, garlic powder, and salt. You can place the fish on the baking tray on top of the foil. Now take the seasoning mixture and rub it generously on both sides of the fish. Sprinkle the remaining spice blend over it, if there is any left. Let it sit 30mins.
Preheat the oven at 375F. Sprinkle oil on to the fish before baking. Place the baking tray and it should take 15-20 mins approx to bake. Turn it once in the middle. Do not over bake it as it will be chewy.
While the fish is baking, you can make the slaw. Mix the slaw ingredients after slicing them thinly.
Once you take it out of the oven, give it a couple of mins to cool down. Sprinkle lime juice on it. Now you are ready to assemble the tacos.
Assemble Tacos: Place the warmed tortilla on a plate, with a few pieces of fish.
Top it with the slaw, avocado if using and drizzle on the crema.