Cook the spaghetti in salted water according to the instructions on the packet until al dente.
Steam the onion cubes in a pan until translucent. Add the minced meat and fry until it is crumbly. Season with salt and pepper. Pour in the vegetable stock and add the spinach. Simmer until the spinach is hot. Stir in the processed cheese and simmer a little. Season to taste and, if necessary, thicken with a little sauce thickener.
Arrange the spaghetti on plates and serve sprinkled with sauce and grated parmesan.