Mixed Grilled Vegetables

INGREDIENTS:
1 1/2 Tablespoon olive oil, plus more for the grates
1 large onion (red or sweet), cut into wedges with root end attached
1 yellow squash, cut into 1/2 inch thick slices
1 zucchini, cut into 1/2 inch thick slices
1 red bell pepper, (ribs & seeds removed), cut into 2 inch wide pieces
1 yellow pepper, (ribs & seeds removed), cut into 2 inch wide pieces
1 large eggplant, cut into 1/2 inch thick slices
1 bunch of asparagus, trimmed off woody ends

PROCEDURE:
1. Place vegetables in a large mixing bowl and drizzle with oil. Season with salt and pepper. 2. Working in batches if necessary, remove from bowl and arrange on preheated and oiled grill.
3. Cook, turning occasionally, until lightly browned and tender.