1. Trim root ends of onions, keeping the bulb heads intact; discard roots. Trim tops so that about 4 inches of upper green portion remain.
2. Cook onions in boiling water 2 minutes or until tender. Drain and rinse with cold water; drain well, and pat dry. Place in a medium bowl.
3. Cook asparagus in boiling water for 4 minutes or until crisp-tender. Drain and rinse with cold water; drain well, and pat dry. Place in another bowl.
4. Heat a grill pan over medium-high heat. Drizzle 1/2 teaspoon oil over onions, tossing to coat. Arrange onions in an even layer in pan, and grill for 30 seconds on each side or until grill marks show. Transfer onions to a platter.
5. Drizzle remaining 1 teaspoon oil over asparagus; toss to coat. Arrange asparagus in an even layer in pan, and cook for 1 minute on each side or until grill marks show. Transfer asparagus to platter. Sprinkle vegetables evenly with salt and pepper. Divide evenly among each of 4 plates; top each serving with about 1 1/2 teaspoons sauce.