Prepare grill for medium heat or preheat oven to 450°. In a large skillet, cook onion in oil over medium-high heat until crisp-tender, 4-5 minutes. Add mushrooms; cook until tender, 4-5 minutes. Stir in tomato paste, basil and oregano; cook until tomato paste starts to caramelize, 6-8 minutes. Stir in broth, stirring to loosen browned bits from pan. Bring to a boil; cook until sauce has thickened, 8-10 minutes. Remove from heat; cool slightly. , Cut each chicken breast into 3 long strips. Divide chicken strips between two 18x12-in. pieces of heavy-duty nonstick foil, placing food on dull side of foil; sprinkle with salt and pepper and top with zucchini. Spoon tomato mixture over zucchini. Fold foil around mixture, sealing tightly., Place packets on grill or in oven; cook until chicken is no longer pink, 15-20 minutes, turning once. Open packets carefully to allow steam to escape. If desired, top with additional basil.