Bring a pot of water to a rolling boil. Add the soba noodles and cook according to package directions, about 3 minutes, until just tender.
Drain the noodles in a colander and rinse under cold water to stop cooking; set aside.
While the noodles cook, slice the chicken breast into thin strips.
Julienne the yellow and red bell peppers and the red onion. Slice the chili pepper. Peel the carrot into ribbons with a vegetable peeler. Drain or slice the baby corn if needed and thaw the frozen green beans.
Heat a wok or large skillet over high heat. Add the sesame oil and swirl to coat.
Add the chicken strips and stir-fry until they begin to brown and are nearly cooked through, about 3–4 minutes.
Add the prepared vegetables (bell peppers, onion, carrot ribbons, baby corn, green beans, and chili) and stir-fry over high heat until vegetables are crisp-tender, about 2–3 minutes.
Add the cooked noodles and soy sauce to the wok. Toss everything together and stir-fry for another 1–2 minutes until heated through and evenly coated.
Remove from heat and serve immediately.
To make a vegetarian version, omit the chicken and proceed using the same method with additional vegetables or tofu.