Saute fish in butter for 3-4 minutes.
Remove fish and add sweet onion, and mushrooms
Add 1/4 C of EVOO and add zucchini. Saute for 1 minute.
Add fish, skin side down and cover for 10-14 minutes to reach 135-140 degrees.
Remove fish, zucchini and mushrooms and cover with foil.
Add lemon juice and reduce braising liquid.
Add salt and pepper to taste.
Spoon over fish and sprinkle with chopped parsley and Lemon Balsamic.