Preheat oven to 350 degrees. Coat a large baking dish with cooking spray. In a small bowl combine zucchini, tomatoes, olive oil, 1/8 Tsp. black pepper and toss to coat. Set aside.
In another small bowl mix together lemon juice and Dijon mustard. Set aside
Season chicken breasts on both sides with 1/8 Tsp. pepper, garlic powder and oregano. Place chicken breasts in baking dish and brush top with mustard mixture. Sprinkle with Parmesan cheese.
Pour zucchini and tomatoes around chicken in baking dish. Bake for 30 minutes or until done.