Sauté the diced onion and the chopped garlic in a little oil, deglaze with the peeled tomatoes. Mash these a little and season with salt, pepper and sugar. Let simmer for about 30 minutes.
In the meantime, cook the spaghetti according to the instructions on the packet.
Remove the stalks from the groundgrass and chop or cut into fine strips. Add to the sauce and let it collapse for a moment. Season again to taste and serve immediately with spaghetti and freshly grated parmesan.