Dry each fillet with a paper towel and season with salt and pepper.
In a shallow baking dish combine flour, garlic powder, onion powder, and dry mustard. Whisk together.
In another shallow baking dish combine eggs, mustard, 1/2 teaspoon salt, and 1/4 teaspoon black pepper. Whisk together until fully combined.
Finally sprinkle panko into a third shallow baking dish.
Dredge each fillet in the flour mixture and shake off excess. Next dredge fillets in the egg mixture, shaking off excess and finally the panko crumbs until fully coated.
Transfer coated fillets to a baking sheet lined with a cooling rack and refrigerate for 30 minutes.
Preheat oil to 350˚F (and oven to 350˚F). Fry fillets for 3 to 4 minutes, flip and continue to fry for an additional 2 to 3 minutes or until golden brown and cooked through. Transfer fried fish back to the baking sheet lined with a cooling rack.
Immediately top fillets with sliced cheese. Transfer fillets into oven and bake for 2 to 3 minutes or until cheese just starts to melt. Remove from oven.
Spread tartare sauce onto the top and bottom of each bun.
Place a cheese covered fillet onto each of the bottom buns and gently press top buns over each fillet. Serve.