3/4 pound hot Italian sausages, casings removed
1 medium onion, chopped
3 large garlic cloves, chopped
1 28-ounce can diced peeled tomatoes
1/4 cup purchased pesto sauce
10 ounces ziti or penne pasta (about 3 cups), freshly cooked
8 cups ready-to-use spinach leaves (about 2/3 of 10-ounce package)
6 ounces mozzarella cheese, cubed
1 cup grated Parmesan cheese (about 3 ounces)