Melt the butter in a medium saucepan over medium heat. Mix in lemon juice, salt, pepper, parsley flakes, and garlic. Bring to a boil. Cook and stir about 10 minutes, until thickened.
Arrange cod fillets in a single layer on a medium baking sheet. Cover with 1/2 the butter mixture, and sprinkle with lemon pepper. Cover with foil.
Bake 15 to 20 minutes in the preheated oven, until fish is easily flaked with a fork. Pour the remaining butter mixture over the fish to serve.
