Bring a large pot of water to a rolling boil over high heat. Add the noodles and boil just until tender (5-7 minutes). Drain the noodles and rinse briefly with cool water. Allow the excess water to drain away.
Combine the chopped cucumber, red pepper, sliced green onion, and chopped peanuts in a large bowl.
Stir together the rice vinegar, sugar, sesame oil, salt, and crushed red pepper in a small bowl until the sugar is dissolved. Pour this mixture over the vegetables and toss to coat.
Add the cooled and drained noodles to the bowl and toss to combine the ingredients and coat in the dressing. Serve immediately or refrigerate until ready to eat.