Peel and finely chop the onion. Grate the parmesan. Dice Fontina, Gorgonzola and Bel Paese. Clean and halve the mushrooms. Roast sunflower seeds in a pan without fat. Cook the pasta in boiling salted water for about 10 minutes. Drain and quench briefly.
In the meantime heat oil in a pan, fry onion and mushrooms, add cream and stock. Bring to the boil and add cheese while stirring. Season the sauce with salt and pepper and simmer at low heat stirring several times. In the meantime clean, wash, quarter, seed and finely dice the tomato. Arrange noodles and sauce on a plate. Sprinkle with diced tomatoes, sunflower seeds and pepper. Serve garnished with basil as desired