Make the marinade by combining the fish, olive oil, dill, garlic, lemon zest, sea salt, and freshly cracked black pepper in a large zip-lock bag, mixing thoroughly. Refrigerate and marinate for 2-4 hours. Side Note: Use only lemon zest for marinating–lemon juice's acid will start to cook the fish.
Preheat the oven to 425 degrees. Spray a glass baking dish with olive oil cooking spray.
Add the lemon juice to the fish in the bag and mix well.
Place the fish in the baking dish and pour the marinade over it. Season the fish well with sea salt and freshly cracked black pepper, then add a tablespoon of butter to each fillet.
Bake the fish by covering with a lid or foil and cook for 10-12 minutes per 1-inch thickness, until just flaky.