Cook the soba noodles or spaghetti according to package instructions. Drain and set aside.
In a large skillet or wok, heat the vegetable oil over medium-high heat. Add the sliced chicken and season with salt and pepper. Cook for about 5-7 minutes, or until the chicken is cooked through and no longer pink.
Add the broccoli, red bell pepper, and carrots to the skillet. Stir-fry for about 3-4 minutes until the vegetables are tender-crisp.
Pour the teriyaki sauce over the chicken and vegetables, stirring to combine. Cook for an additional 2-3 minutes until everything is heated through.
Add the cooked noodles to the skillet and toss everything together until well combined.
Serve hot, garnished with chopped green onions and sesame seeds if desired.