Toast the sesame seeds in a dry skillet over medium heat, stirring frequently, until golden and fragrant; transfer to a small bowl and set aside.
Place half of the teriyaki sauce in a bowl and toss the chicken strips in it to coat; let marinate briefly while you heat the pan.
Heat the canola or coconut oil in a large skillet or wok over medium heat. Add the chicken strips and cook about 4–5 minutes per side, until golden and cooked through; remove chicken and set aside.
Add the green beans and the 1/4 cup chicken stock to the same pan, cover, and cook about 5 minutes until the beans are crisp-tender.
Uncover and add the sesame oil and sliced bell peppers; cook uncovered about 4 minutes until peppers are tender-crisp.
Add the minced garlic and the remaining teriyaki sauce to the pan and cook, stirring, about 30 seconds until fragrant.
Return the cooked chicken to the pan, toss to combine, and cook 1 minute more until everything is warmed through.
Remove from heat, sprinkle with toasted sesame seeds, and garnish with chopped scallions or cilantro; serve with brown rice or noodles if desired.