Preheat your oven to 400°F (200°C).
In a mixing bowl, combine breadcrumbs, garlic powder, paprika, salt, and black pepper.
Coat each fish fillet with the breadcrumb mixture, pressing gently to adhere.
Place the coated fish fillets on a baking sheet and bake for 15-20 minutes, or until the fish is cooked through and the coating is golden brown.
While the fish is baking, mix mayonnaise and lemon juice in a small bowl.
Toast the sandwich buns if desired.
Assemble the sandwiches by spreading the lemon mayo on the buns, adding a fish fillet, and topping with shredded lettuce and sliced tomato.