Cook noodles according to package directions. Drain, then rinse under cold water until cool. In a medium bowl, stir together peanut butter, lemon juice, chili sauce, and pepper flakes. Add a splash of coconut milk and stir. Continue adding coconut milk and stirring until mixture is the consistency of pudding. Pour the peanut butter mixture over the noodles and toss until noodles are completely coated. To serve, place noodles on a plate. Top with cucumber, peanuts, and toasted sesame seeds.