Cook the egg noodles according to package instructions.
Prepare the chicken by cutting it into bite-sized pieces.
Heat vegetable oil in a large frying pan or wok over medium-high heat.
Add the chicken to the pan and cook until browned.
Add the sliced bell pepper and snap peas to the pan.
In a small bowl, mix soy sauce, mirin, and cornstarch to make the teriyaki sauce.
Pour the teriyaki sauce over the chicken and vegetables in the pan.
Add the cooked egg noodles to the pan and toss everything together.
Sprinkle sesame seeds and chopped green onions on top before serving.