Take the mushrooms and cut them up to your liking... there are no rules about size. Heat a saute pan to medium high and add about a tablespoon of EVOO. Add the mushrooms, finely diced red onion, garlic, and S&P. Mix em up real good and cook them to your desired doneness. Once they get where you want them to be, dump them out and put the butter in the pan and get the good bits on the bottom of the pan mixed in with the butter. Lower the heat to medium low then add the juice from a half of a very small lemon, and about 3 tablespoons of juice from a jar of cocktail olives. Toss in the fish fillets and dust them lightly with salt and pepper on one side only. Let the fish poach, about four minutes a side. When you turn the fish over, add the scallops. Cook the scallops about six minutes all together.
When I made this dish on a recent trip to south Texas and Louisiana, The sauce on the fish was made from the pan drippings and some etouffee base I had in the fridge. This dish needs no gravy. We tried it two ways.... don't let the photo fool you.
Serve this fish, with the mushrooms on the side or over the fillets, and a salad for a light meal. It would be great with a rice pilaf as well.