1. Preheat grill to medium. Cut 6 12-by-18-inch pieces of heavy-duty foil.
2. In a large bowl, whisk oil, vinegar, garlic, seasoned salt and pepper. Add vegetables; toss to coat. Divide vegetables evenly among foil pieces. Drizzle with any remaining dressing.
3. Fold long sides of foil toward each other, crimping edges to seal. Fold and crimp remaining edges, forming a sealed packet.
4. Place packets, seam side up, on grill. Close grill and cook for 20 minutes. To check for doneness, remove one packet from grill, open carefully and taste a vegetable: It should be crisp-tender. Carefully open packets and serve.