Preheat oven to 400 degrees F and lightly grease a 9x13 baking dish.
Lay 4 portions cod fish out in the prepared baking dish. Season fish with 1/2 teaspoon salt and 1/4 teaspoon black pepper.
In a small bowl, stir together the 1/4 cup softened butter, 2 tablespoons freshly grated Parmesan cheese, 1 tablespoon all-purpose flour, 1 tablespoon minced garlic, 1 teaspoon dried basil, 1/2 teaspoon onion powder, 1 teaspoon dijon mustard, and 1/4 cup lemon juice.
Top each filet with a large spoonful of the butter mixture.
Bake in the preheated oven for about 10 minutes. Actual cooking time will depend on the thickness of your fish. The fish is done when it flakes easily with a fork.