Cut the fish fillets into burger-sized pieces.
In a shallow bowl, mix the flour, garlic powder, paprika, salt, and black pepper.
In another bowl, pour the buttermilk.
In a third bowl, place the breadcrumbs.
Dip each piece of fish first into the flour mixture, then into the buttermilk, and finally coat it with breadcrumbs.
In a large skillet, heat about 1 inch of vegetable oil over medium-high heat.
Once the oil is hot, carefully add the breaded fish pieces in batches, frying for about 3-4 minutes on each side or until golden brown and cooked through.
Remove and drain on paper towels.
Toast the hamburger buns lightly.
Assemble the burgers by placing a piece of fried fish on the bottom half of each bun, adding lettuce, tomato slices, and a generous dollop of tartar sauce.
Top with the other half of the bun.
Serve immediately while hot and crispy.