Soak the noodles according to the package and drain. Rinse with cold water, drain. Cut into 3/4" long pieces with scissors.

Combine lime juice and next 6 ingredients in a large glass bowl. Stir in noodles, cilantro, green onion, avocado and cucumber. Cover and refrigerate for 30 minutes. Top noodle mixture with tuna; stir tuna into noodle mixture just before serving. Sprinkle with sesame seeds.