Preheat the oven: Set your oven to 400°F (200°C). Line a baking dish with parchment or lightly grease it.
Pat dry the cod: Use paper towels to remove extra moisture. Dry fish browns and flakes better.
Make the lemon-herb mixture: In a small bowl, combine lemon zest, lemon juice, olive oil (and butter if using), garlic, parsley, dill, thyme, paprika, salt, and pepper.
Stir well.
Season the fillets: Place cod in the baking dish, leaving a little space between pieces. Spoon the mixture over the fish, coating all sides. Top with a few lemon slices.
Bake: Cook for 12–15 minutes, depending on thickness.
Cod is done when it flakes easily with a fork and is opaque all the way through. Thicker pieces may need a couple more minutes.
Optional quick broil: For a touch of color, broil on high for 1 minute at the end. Watch closely.
Finish and serve: Let the fish rest for 2 minutes.
Taste and add a pinch of salt or a squeeze of lemon if needed. Garnish with extra herbs and serve.