Turn on your oven to 350 degrees. Brown the butter in a medium-size saucepan. Add the celery (or ground celery), garlic, onion, Old Bay and salt and pepper. Simmer for 2 or 3 minutes.
Stir the cup of seafood into the browned butter sauce and simmer for another 2 or 3 minutes.
Hollow out the centers of your mushrooms. Dice the clean hollowed out remains and put this in a medium size bowl.
Crumble the dry gluten free bread and place it in the bowl with the diced mushroom remains. Beat the egg and incorporate into the diced mushroom and breadcrumbs. Add the parmesan cheese if you choose to use this.
Slowly pour the seafood mixture over the diced mushroom and breadcrumb mixture. Stir until well incorporated.
Stuff each mushroom to the brim! Place in the oven and cook until the tops are golden brown and the cheese melts.