Dice the onion and mince the garlic. Cook both in a large pot with one tablespoon of olive oil over medium-low heat until soft and transparent (about 5 minutes).

Add the Italian sausage to the pot and cook through (breaking it up into pieces as you cook). Add the tomato paste, stir and cook for about 2-3 minutes more or until the tomato paste takes on a slightly darker color. Add the diced or crushed tomatoes, salt, and sugar. Stir and heat through.

Preheat the oven to 350 degrees. Bring a large pot of water to a boil (this can be done while you’re preparing the sauce in step 2). Cook the pasta according to the package directions (boil for 7-10 minutes). Drain the cooked past and then stir into the meat sauce.

Prepare an 8×8 inch casserole dish by coating with non-stick spray. Add half of the spaghetti mixture to the dish. Sprinkle withe feta cheese. Add the rest of the spaghetti, sprinkle with parmesan cheese, and then top with mozzarella.

Bake the spaghetti for 30 minutes in the 350 degree oven. Let rest for about 10 minutes before cutting into eight pieces and serving.