Preheat oven to broil and raise rack to top.
Prepare your fish by first patting dry.
Season both sides of fish with salt and pepper.
Add onion powder and garlic powder to flour. Mix until combined.
Dredge each fillet in the flour, shaking off any excess, dip in the beaten eggs, and finally coat in panko breadcrumbs.
Heat one inch of oil in a large skillet over medium heat, reaching 350 degrees F. Once hot, add the fish fillets and cook until golden brown and crispy on both sides. This should take about 2-3 minutes per side.
While the fish is cooking, place your brioche buns on a baking sheet and toast under the broiler until golden brown.
Lay the cooked fish on paper towel to absorb any grease.
To assemble the sandwiches, spread a generous amount of tartar sauce on the top and bottom half of each toasted brioche bun.
Lay a piece of cheddar cheese on the bottom half and place the crispy fish on top.
Lay a piece of lettuce, followed by a handful of shredded red cabbage and the top half of your brioche bun.
Serve your delicious crispy fish sandwiches with lemon wedges and chips on the side if desired.