Preheat the oven to broil at 450°F (230°C). Set the top rack in the oven to be about 10 inches (25 cm) from the top.
Line a cookie sheet with parchment paper and grease the sheet with the fat of choice. Lay your prepared fish fillets down.
Using a spice grinder or mortar & pestle, grind the fennel, nigella, and sea salt into a powder. Sprinkle the spice mixture on to your fish fillets, coating evenly.
Place the fish into the preheated oven, baking for 8-12 minutes, depending on the thickness of the fish. When you can easily flake the fish, it is cooked through. Take it out of the oven and
Serve immediately!