Cut the onion into half rings.
Cut the chicken fillet into strips.
Cut the bell pepper into thin strips.
Cook soba according to package directions until al dente.
Heat a frying pan with vegetable oil. Fry the chicken over high heat until golden and half-cooked, 3-4 minutes. Turn the chicken over a couple of times. If you have enough skills, you can turn the chicken over by tossing it.
Transfer the chicken to a separate bowl. In the same pan, fry the onion and bell pepper over high heat for 3-4 minutes.
Add chicken to vegetables and pour soy sauce over everything. Stir until all ingredients are coated with soy sauce. Fry vegetables until sauce evaporates completely for 1-2 minutes.
Add the cooked buckwheat noodles to the pan and season with teriyaki sauce. Season with pepper to taste. Mix all the ingredients carefully with tongs or two spatulas so as not to break the noodles.
Sprinkle the finished soba with chicken and vegetables with chopped green onions and sesame seeds. Enjoy.