Arrange the lemon slices in the bottom of a 9-inch x 13-inch baking dish. Place the cod fillets over the lemon slices and lightly coat with non-stick cooking spray.
In a small bowl, stir together the softened butter, salt, garlic, lemon zest, and ½tablespoon of lemon juice until well combined. (see note)
Rub the butter all over the fish fillets. Sprinkle lightly with pepper and paprika.
Bake for 13 minutes or until the internal temperature reaches 140 degrees F.
Remove from the oven, sprinkle with chopped parsley, and serve warm.
Notes
If the butter is not soft enough to spread easily, place it in the microwave and heat on low in 5-second intervals until ready. Do not melt the butter.