Rinse asparagus, and break or cut off tough ends.

Cover the bottom of a large frying pan with water. Top with lid and bring to a boil.

Add asparagus, cover, and cook for 2 minutes or until al dente.

Transfer asparagus to a cutting board.

Rinse out frying pan, dry, and add a small amount of olive oil.

When heated, add mushrooms and sauté until tender, approximately 5 minutes.

Transfer mushrooms to a large mixing bowl.

Add a small amount of oil to same frying pan, and add onion.

While onions cook, cut asparagus into bite-sized pieces and add to mixing bowl.

Sauté onions until tender, about 5 minutes; transfer to mixing bowl.

Top with balsamic vinegar and toss well to coat.

Season with salt and pepper as desired.

Serve immediately.