Chop the filet into 4-inch pieces. They need to be about 4″ x 3″ in length and width. We want nice medium sized pieces.
Blend cilantro leaves, coconut, garlic cloves, curry leaves, lemon juice, tamarind concentrate, onion, salt, Serrano peppers, and 4 tablespoon water in a blender.
Once blended, mix Kashmiri chili powder, ground cumin, ground coriander, ground ginger, ground turmeric, garam masala, and mango powder with the blended paste.
In a mixing bowl, coat the fish well with the marinade.
Let the fish sit in the marinade for 30 minutes covered with a lid. If you have time leave it overnight in the refrigerator.
When ready to cook line the air fryer basket with aluminum foil. Make sure the basket does not stick out beyond the basket edge. ALSO, THIS IS KEY! DO NOT COVER THE BASKET BOTTOM COMPLETELY. To cook the food well, air needs to flow through the basket. If you cover the bottom of the basket, this reduces the airflow.
Brush/ grease the aluminum foil generously with oil. Preheat at 350°F for 5 minutes.
When the air fryer is preheated, place the fish in a single layer. Set the time and temperature (390°F for 10 minutes).
When done, flip the pieces of fish in the basked and repeat for another 7 minutes.
Repeat the process until you run out of fish.