How to Make It
Soak noodles according to package directions; drain. Rinse with cold water; drain. Cut into 3/4-inch-long pieces using scissors.
Combine lime juice and next 6 ingredients in a large glass or ceramic bowl. Stir in noodles, cilantro, green onion, avocado, and cucumber. Cover and refrigerate at least 30 minutes. Top noodle mixture with tuna; stir tuna into noodle mixture just before serving. Sprinkle evenly with sesame seeds.