Make a paste with Italian seasoning and olive oil. Salt and pepper the cavity, squeeze some lemon juice into it, then coat the inside with the paste. Grease foil with butter, put thinly sliced onion down and sprinkle with pepper. Lay fish on top, put onion and pepper on top side. Loosely wrap the foil around the fish, but seal it tight. Bake for @ 20 minutes at 400*. You can peel the top meat from the bones with a fork, then pull the bones out of the rest. You can do this on a grill or oven.
Mix in some lemon zest with the Italian seasoning and sprinkle a bit on both sides of the fish. Almost forgot about that part.