1. Bring a large pot of water to a boil.
2. Place the chicken on a microwave-safe plate and cover with a paper towel. Microwave at HIGH for 2 minutes or until heated through.
3. Add soba noodles to boiling water and cook for 5 minutes; drain well.
4. Whisk together the next 4 ingredients (through mustard). Add the chicken, carrots, and scallions to the sauce mixture.
5. Toss the hoisin-chicken mixture with the noodles until well coated. Divide noodles and chicken among 4 plates; sprinkle peanuts on top.