In a large skillet over medium heat, melt 1 tablespoon butter and olive oil. Add mahi mahi and season with salt and pepper. Cook until golden, 3 minutes per side. Transfer to a plate.

To skillet, add remaining 2 tablespoons butter. Once melted, add garlic and cook until fragrant, 1 minute, then stir in lemon zest and juice and parsley.

Return mahi mahi fillets to skillet and spoon over sauce.

Garnish with more parsley and serve.