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 tbsp of butter and onion and saute for 5 minutes.
Add garlic, chopped and pureed roasted peppers and keep cooking for another 5 minutes.