Soak mushrooms in water until hydrated, 15 to 20 minutes. Drain and place in a saucepan over medium heat; boil for 2 minutes. Drain and let cool.
Combine lime juice, soy sauce, sesame oil, ginger, sugar, and chile pepper in a bowl. Toss in cucumber, mushrooms, and sesame seeds. Chill for at least 1 hour before serving.
