In large skillet, brown ground beef and onion until beef is thoroughly cooked. Drain. Stir in seasoning mix, water, zucchini, corn and tomatoes. Bring to a boil. Stir in rice. Reduce heat to low; cover and simmer 5 to 7 minutes or until liquid is absorbed, stirring occasionally.
Remove from heat. Fluff mixture with fork; sprinkle with cheese. Cover; let stand 3 minutes or until cheese is melted. If desired, garnish with diced red bell pepper and jalapeño chiles.