Drop the soba noodles into boiling, salted water and cook for approximately 5 minutes or until just tender, taking care not to overcook them. Strain the noodles and immediately rinse thoroughly in cold running water. Set aside in strainer until ready to use.
Whisk the dressing ingredients together in a large mixing bowl, add the soba noodles and toss until coated. Mix in the carrots, cabbage, Mandarin orange slices, radish and spinach.
Transfer into a large serving bowl and garnish with the sliced avocado, cilantro, green onion and sesame seeds.