Butter a large baking dish, and set aside.
Preheat the oven to 325°F.
Whisk together the melted butter, lemon juice, garlic, onion powder, salt, and pepper.
Place the flounder fillets into the prepared baking dish.
Pour the butter mixture over the flounder fillets.
Sprinkle the fillets with smoked paprika.
Bake for 15 to 20 minutes or until the fish flakes easily with a fork.
Serve hot with steamed vegetables or a salad.
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