Preheat oven to 350F degrees. Spray a 9X13 baking dish with nonstick spray. Prepare pasta accodring to directions. In a medium sauce pan, brown ground beef with onion (if using). After beef is browned and crumbled, drain excess grease. Put back in pot and pour in on jar of the spaghetti sauce. Keep mixture on low until pasta is done. When pasta is finished, drain well. You want the pasta as dry as possible. Put pasta back in large pot (with heat off) and pour in jar of alfredo sauce. Combine until thoroughly coated.
Pour pasta mixtures into bottom of 9X13 dish.
Cover pasta with spaghetti sauce mixture.
Sprinkle top with mozzarella cheese.
Cover with aluminum foil and bake for 15 minutes. I like to spray the inside of my foil with nonstick spray so the cheese doesn't stick to it. Or you could use nonstick aluminum foil.
Remove foil and bake for another 15 minutes until cheese is melted and bubbly. Let rest for about 5 minuts after taking out of oven.