In a cast iron or heavy bottomed skillet, 1 tablespoon olive oil on medium-high heat. Pat the fish dry and sprinkle with cayenne, salt, and pepper. Carefully place into the skillet and reduce heat to medium. Cook for about 3 minutes on both sides, until it's no longer translucent.
Transfer the fish to a plate, top with the lime juice, and flake apart with a fork.
In a small bowl, combine all ingredients for the mango salsa. Set aside.
In a separate small bowl, combine the sour cream and lime juice.
Heat up your tortillas either on an open flame or in a skillet.
To assemble, divide the fish evenly across all four tacos, add your desired amount of salsa and crema on top, and finish with some slices of avocado.
Enjoy!