In large soup pot, brown sausage with onions. When sausage is cooked through, drain off all excess oil. Add water, pizza sauce, diced tomatoes, Italian seasoning, garlic, mushrooms and tortellini. Simmer over medium heat about 30 minutes, stirring occasionally. If soup is too thick, add tomato juice or water to thin.
Just before serving, place mozzarella cheese in bottom of bowl. Pour hot soup over top and garnish top with Parmesan.
NOTE: For best results, use prepared pasta with mixed cheeses found in the refrigerated section of your grocery store.Makes 1 gallon Source: