HEAT oil in large pot over medium heat. Add peppers and onions; cook for 3 minutes. Add potatoes and broth; bring to a boil. Cook over medium heat for 15 minutes or until tender. Stir flour mixture into pot; continue cooking for 2 minutes. Stir in evaporated milk. Bring to a boil again, stirring occasionally. Season to taste.
TO SERVE: Divide tomatoes and cheese among 8 bowls. Pour soup into bowls. Garnish with sliced green onions, chopped cilantro or parsley, if desired.