How to Make It
Cut the fish into 1 1/2-inch pieces. In a medium bowl, stir 1/4 teaspoon salt into the egg. In another medium bowl, stir together the almond flour, chile powder, cayenne, and 1/4 teaspoon each of salt and pepper. Dip the fish into the egg, letting any excess drip off, then coat it in the almond flour mixture.
Line a baking sheet with paper towels. Heat about 1 inch of oil in a large heavy skillet over medium-high heat until it reaches 375°. Fry fish, turning occasionally, until golden and cooked through, 4 to 6 minutes. Transfer the fish to the paper towel–lined baking sheet to drain briefly.
In a serving bowl, stir together the mayonnaise and the relish until combined. Serve the fish with the tartar sauce.