Bring a pot of water to a boil and cook the soba noodles for 4-5 minutes until al dente, then drain and rinse immediately with cold water.
Poach the chicken breast in simmering water for 12-15 minutes until the internal temperature reaches 165 degrees Fahrenheit, then shred it into thin strips.
In a small bowl, whisk together the peanut butter, sesame oil, tamari, rice vinegar, grated ginger, and garlic powder until the dressing is smooth.
Slice the cucumber and red bell pepper into thin julienne strips to match the shape of the noodles.
In a large mixing bowl, combine the chilled soba noodles, shredded chicken, cucumber, and bell pepper.
Pour the peanut dressing over the salad and toss thoroughly to ensure all ingredients are evenly coated.
Garnish with thinly sliced green onions and serve chilled.