Toast sesame seeds in a dry skillet over medium heat, stirring frequently.
Coat chicken strips in half the teriyaki sauce. Add oil to a pan or wok over medium heat. Cook for about 4-5 minutes per side until golden and cooked through.
Add green beans and water or chicken stock to the pan. Cover and cook for about 5 minutes, until beans are crisp-tender. Add sesame oil and peppers to the pan with the beans. Cook uncovered for about 4 minutes. Add garlic and remaining teriyaki sauce, cook for an additional 30 seconds.
Return chicken to pan and stir. Cook for one minute, until warmed. Remove from heat and sprinkle with toasted sesame seeds. Garnish with scallions or cilantro.