Heat olive oil in a large heavy skillet over medium-high heat. Place the sausage in the pan and brown well on both sides. Add the onion and garlic; cook, stirring frequently until both are translucent.

Now add the tomato sauce, diced tomatoes, oregano, Italian seasoning, salt and pepper; stir to combine and bring to a boil. Reduce heat to low, cover and simmer for 15 minutes.

Add the cooked pasta and baby spinach; stir. Cook until the spinach wilts then add the mozzarella stirring until cheese just melts. Top with grated parmesan cheese.