Lightly brush vegetables with 1 tablespoon of the oil. For a charcoal grill, place vegetables on the rack of the grill over medium-hot coals. Cover and grill for 3 to 5 minutes for asparagus, turning once, and about 10 minutes for the zucchini, sweet pepper, and onion, turning once, or until vegetables are tender. Remove and cool slightly. (For a gas grill, preheat grill. Reduce heat to medium-high. Add vegetables to grill rack and grill as above.)
Cut vegetables into 1/2-inch pieces and toss with pasta in a large bowl. Add remaining oil, balsamic vinegar, salt, and black pepper to pasta mixture; toss to coat. Makes 4 servings.