Preheat the Oven: Set your oven to 400°F (200°C). Lightly grease a baking dish or line it with parchment paper for easier cleanup.
Prepare the Lemon Butter Mixture: In a small mixing bowl, whisk together the melted butter, olive oil, minced garlic, lemon juice, and lemon zest until thoroughly combined.
Season the Cod Fillets: Arrange the cod fillets in the prepared baking dish. Lightly season both sides with salt and freshly ground black pepper.
Apply the Lemon Butter Sauce: Evenly drizzle the lemon butter mixture over the seasoned cod fillets, ensuring each piece is well-coated.
Bake: Place the baking dish in the preheated oven and bake for 12 to 15 minutes, or until the cod turns opaque and flakes easily with a fork. Cooking time may vary depending on the thickness of the fillets.
Garnish and Serve: Once baked, remove the dish from the oven. Sprinkle the cod with chopped fresh parsley and, if desired, garnish with additional lemon slices. Serve immediately.