Dice the onion, zucchini and bell pepper. Briefly fry the onion in a saucepan with a little olive oil, then add the zucchini and peppers and sauté for a few minutes. Then add the tomatoes, bring to the boil and simmer for a while.
Bring a saucepan of water to the boil, add salt and cook the spaghetti until cooked.
Towards the end of the cooking time, add the spaghetti, cream and yoghurt to the sauce and season with the spices. Dice the mozzarella.
Pour off the spaghetti water and distribute the spaghetti on the plates, pour the sauce over it and garnish the dish with the mozzarella.