In a Dutch oven cook sausage until there is no pink; drain. Add onion, green pepper, mushrooms, and garlic over medium heat. Cook until vegetables are tender.
Stir in the salsa, pizza sauce, diced tomatoes, pepperoni slices, and water.
Add pizza seasoning, salt, and pepper. Bring to a boil. Reduce heat; cover and simmer until heated through, about 20 minutes.
Use a ladle to scoop soup into bowls. If desired, garnish with sliced black olives, sliced green onions, and sprinkles of mozzarella. If desired, serve with breadsticks.