Prepare chicken tortilla soup by sautéing chicken breast, onions, peppers, and garlic in olive oil. Cook chicken breast on a medium heat until cooked through. Remove from heat and set aside. Add chicken broth, tomatoes, and water to a large pot and simmer for 15-20 minutes. Stir occasionally. Add chicken, cheese, and corn. Stir until cheese the is melted. Top with avocado and sour cream if desired. Serve with tortilla chips, cornbread, or salsa.