Asparagus and Roasted Bell Peppers

This is from one of my favorite Williams Sonoma cook books, "Easy Vegetarian"

ingredients
3 red bell peppers
2 red onions
1 lb. asparagus, trimmed
1/3 cup olive oil
2 tablespoons balsamic vinegar
Sea salt and freshly ground black pepper
2 oz. Parmesan cheese, cut into shavings, for serving

preparation
Cut the bell pepper flesh away from the core in flat pieces to make grilling easier. Put the pepper pieces skin-side down on a preheated stove-top grill pan and cook until the skin is blistered and turning black. Transfer the peppers to a small bowl and cover the bowl with plastic wrap - let steam for 10 minutes. When cool enough to handle, peel the skins away from the flesh.

Cut the onions into wedges, leaving the root end intact to hold them together. Add to the grill pan and cook for 4 minutes on each side, then add the asparagus to the grill pan and cook for about 3 minutes or until just soft.

Put the peppers in a bowl with the onions, asparagus, olive oil, vinegar, salt and pepper. Toss to coat, then serve warm or at room temperature with shavings of Parmesan cheese.