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 lightly browned.
Add the broccoli, bell pepper, and carrot to the skillet. Stir-fry for another 3-4 minutes until the vegetables are tender-crisp.
Pour the teriyaki sauce over the chicken and vegetables, stirring to coat everything evenly. Cook for an additional 2 minutes until the sauce is heated through.
Add the cooked noodles to the skillet, tossing everything together until the noodles are well coated with the sauce and heated through.
Remove from heat and garnish with sliced green onions and sesame seeds, if using. Serve immediately.