BROWN meat in large nonstick skillet on medium-high heat; drain. Add onion; cook and stir until tender. Stir in dressing mix. Reduce heat to medium-low. Add zucchini, tomatoes and corn; mix lightly. Cover; simmer 5 minutes.
STIR in water. Bring to boil on medium-high heat. Stir in rice; cover. Reduce heat to medium-low; cook 5 minutes. Remove from heat; stir. Cover and let stand 5 minutes. Fluff with fork.
SPRINKLE with cheese; cover. Let stand 5 minutes or until cheese is melted.