1. In a bowl place tuna and gently break into pieces with fork.
2. In a small saucepan combine vinegar, onion, dill seed, bay leaf and mustard; bring to boil. Pour marinade over tuna; refrigerate several hours or overnight.
3. Just before serving, drain tuna; combine with celery and mayonnaise. Serve on lettuce bed and garnish with tomatoes and asparagus.