Preheat the oven to 350 degrees F. Coat a 9"x13" pan with cooking spray.
Boil water and cook the pasta according to the package instructions. Drain and set aside.
Heat the olive oil in a large pan over medium high heat.
Add the sausage to the pan and cook it for 3-4 minutes, breaking it up into small pieces with a spoon. Add the onion to the pan, and cook for 5 more minutes or until the sausage is cooked through and the onion has softened.
Add the garlic and cook for 20 seconds. Add the marinara sauce and tomato sauce bring the sauce to a simmer.
Let the sauce simmer for 5 minutes or until just thickened
Toss the cooked pasta with the sauce.
Pour the pasta mixture into the prepared pan and top with mozzarella cheese.
Bake covered for 20 minutes, then uncover and bake for another 15-20 minutes or until pasta is bubbly and cheese is melted and browned.
Serve hot and enjoy!