Peel and finely dice the onion and garlic. Heat 2 tablespoons of oil in a large pot. Fry the onion and garlic in it. Add the tomatoes and chop a little with a spatula. Add 750 ml water, season with chili flakes, salt, pepper and sugar.
Bring to the boil and add the pasta. Let simmer for about 5 minutes. Wash and clean the mussels. Sort out open mussels.
Add the mussels to the noodles and simmer covered for about 8 minutes, stirring from time to time. Wash fish fillet, dab dry and cut into cubes. Wash prawns, dab dry. Heat 2 tablespoons of oil in a frying pan, first fry the prawns, then the fish in it while turning.
Season with salt and pepper. Wash the basil, dab dry. Pluck leaves and cut into strips. Flavour pasta again. Carefully fold in shrimps and fish, arrange and sprinkle with basil.