Bring a large pot of water to boiling and cook the soba noodles according to package instructions. Drain and rinse in cold water.
Rinse and chop all the vegetables. Set aside in a large bowl.
For sesame sauce, whisk all ingredients in a small bowl until combined. Add additional water if needed. (The sesame oil is optional but is recommended for flavor. )
To assemble, toss veggies with the sauce until coated. Add in soba noodles and mix gently until all combined. Taste and add more seasonings (lime juice, sesame oil, tamari/soy sauce) as needed. Garnish with toasted sesame seeds and green onions and serve.