Pizza Soup

1 tablespoon olive oil
1 medium onion, finely chopped
1/2 cup fresh mushrooms, sliced
1/4 cup green bell peppers, thinly sliced
1 cup stewed tomatoes, undrained
1 cup beef stock
8 ounces pepperoni, thinly sliced
1/2 teaspoon dried basil
1/2 teaspoon dried oregano
1 dried bay leaf
Salt and pepper, to taste
1 cup mozzarella cheese, shredded

Warm olive oil in a large, deep skillet over medium heat. Saut