1. Place chicken cutlets in a shallow pan or wide bowl.
2. In a small bowl, combine red wine vinegar, orange juice, lemon juice, garlic, mustard, olive oil and pepper. Pour half of the vinaigrette over cutlets and let marinate in fridge for at least one hour.
3. Heat a grill pan (or grill) until very hot. Grease with nonstick cooking spray. Season the string beans, zucchini, and mushrooms with salt. Cook string beans on grill pan for 5 minutes, until cooked but still very crisp. Add zucchini, mushrooms, and red pepper and cook until tender, about 10 minutes (if zucchinis are large, you may need to do this in batches if you are using a grill pan). Remove from pan. Keep warm.
4. Remove chicken from marinade and place on grill pan. Cook for about six to eight minutes on each side, until browned.
5. Plate the chicken and vegetables. Pour remaining reserved vinaigrette over vegetables. Top with sesame seeds (optional). Serve.