Combine garlic powder, 1/4 teaspoon salt, and 1/8 teaspoon pepper in a small bowl; sprinkle chicken with garlic powder mixture. Place the chicken on a broiler pan coated with cooking spray, and broil for 6 minutes on each side or until chicken is done. Remove the chicken from pan, and keep warm.
Heat olive oil in a large nonstick skillet over medium-high heat. Add 1/4 teaspoon salt, mushrooms, zucchini, and minced garlic; sauté 2 minutes. Add 1/8 teaspoon black pepper, tomato, onion, basil, and vinegar; sauté 3 minutes. Serve the vegetable mixture over chicken; sprinkle with cheese.