Chop the onions and garlic and sauté them in olive oil with a few leaves of basil. Add the cooked pasta and fry for a few minutes over high heat. The tomatoes and the feta are added diced. Fry the whole thing over medium heat until the cheese is well spread. Season to taste with salt and pepper.
The whole thing goes even faster if you use the recipe for recycling spaghetti leftovers.