Heat oil in large saucepan or Dutch oven over medium heat until hot. Add onion and garlic; cook and stir 2 minutes or until tender. Stir in zucchini, summer squash and bell pepper; cook and stir 2 minutes or until crisp-tender.
Add broth and macaroni rings; mix well. Bring to a boil. Reduce heat; cook over medium heat for about 7 minutes or until macaroni is tender, stirring occasionally.
Add spinach; cook 1 minute or just until wilted. To serve, spoon soup into individual soup bowls. Top each with cheese.