With a small knife remove the beards from the mussels and leave soaking in water for 1 hour.

Clean the clams with a hard brush to get rid of the sand attached to the shell. Wash them with running water and soak in water with salt for 2 hours. Clean the clams with fresh water again.

In a deep pot heat the oil and sauté the onions and garlic together.
Add wine, water, mussels, and clams. Cover the pot. Cook until mussels and clams are open.
In the meantime, melt the butter in a frying pan and sauté the flounder. Half cook, add the shrimps.

Cover and finish cooking.
Once the mussels and clams are cooked, remove half of the shelf. Add peppers, parsley, scallions, and ground pepper to the liquid in the pot.

Serve the fish with mussels and clams. On top arrange the shrimps. Pour the liquid with vegetables and herbs on top of the seafood.