Cook asparagus until slighly tender but still crisp (about 3 mins.). Drain and rinse with cold water.
In large bowl combine asparagus, tomatoes, mushrooms and pepper.
In measuring cup, combine oil, vinegar, garlic, tarragon, salt and pepper. Mix well and pour over vegetables. Toss. Cover and refrigerate for 2 hours before serving. Serve with feta cheese, if desired.