Heat a lug of olive oil in a pot. Sear the scampi and set them aside.
Season the grouper fillet, coat them in flour, fry them on both sides and set them aside.
In the same oil, gently fry the finely chopped garlic, onion and pepper. When the vegetables have taken on some colour, add the tomato sauce. Continue frying for 5 more minutes to concentrate the flavours; add the fish stock.
Peel and break up the potatoes, add them to the pot and let everything simmer for 15 minutes.
Chop up the hazelnuts, croutons and parsley and add them to the pot.
Add the scampi and the grouper, salt to taste and let everything cook for 10 more minutes. The grouper stew with scampi is ready to serve.