Melt 2 tbsp. of butter in a large, non-stick skillet and fry the fish for 3-4 minutes on each side, until cooked through.
Season the fish with salt and pepper, remove from the skillet and set aside. To the same pan, add the remaining 1 tablespoon of butter and onion and saute for 5 minutes.
Add garlic, chopped and pureed roasted peppers and keep cooking for another 5 minutes.
Add heavy cream and Parmesan cheese. Turn off the heat, stir, and taste if the sauce needs more salt.
Return the fish to the pan and cover with sauce.
Garnish with chopped parsley and grated Parmesan cheese.
Notes
Home-baked and store-bought roasted peppers will work well in this recipe.