1. Combine olive oil, vinegar, basil, rosemary, thyme, salt, and pepper.
2. Place onion, red pepper, zucchini, corn, and mushrooms in plastic bag with zippered closing; add olive oil mixture to bag. Seal; shake or turn bag to coat. Marinate in refrigerator 2-4 hours.
3. Remove vegetables from marinade; reserve marinade. Thread vegetables onto 8 10-inch skewers. Grill or broil 4-5 inches from heat, turning, and basting with reserved marinade, 10 to 15 minutes, or until vegetables are tender.