Set up for success. Place a wire rack over a baking sheet and line a second area with paper towels (helpful for quick draining). Pat the walleye fillets very dry with paper towels this is key for crisp breading.
Make the wet dip. In a shallow bowl, whisk together the buttermilk and eggs until smooth.
Make the breading mix. In another shallow bowl, combine flour, cornmeal, panko, paprika, garlic powder, onion powder, salt, pepper, and cayenne (if using).
Bread the fish. Dip each fish fillet into the buttermilk mixture, let excess drip off, then press into the breading mix. Flip and press again so it’s fully coated. Place breaded fish on the wire rack while you finish the rest.
Heat the frying oil. Add 1/2 inch of oil to a heavy skillet or Dutch oven. Heat to 350°F (175°C) using a cooking thermometer (this is the difference between greasy and crisp!).
Fry in batches. Carefully lay fish into the hot oil, without crowding. Fry 2–4 minutes per side (depending on thickness) until deeply golden and crisp.
Drain and keep crisp. Move fried fish to the wire rack (not straight onto paper towels this helps keep the crust crunchy).
Check doneness. Fish should flake easily and reach 145°F (63°C) in the thickest part if you use an instant-read thermometer.
Serve. Hit with a squeeze of lemon and serve warm with tartar sauce.