In a bowl, combine the chicken strips, 1/2 tsp garlic powder, 1/2 tsp salt, 1/4 tsp black pepper and 1 tbsp cornstarch; toss to coat and set aside.
Heat a large non-stick skillet or wok over medium heat and add 1 tbsp butter; add the green beans and stir-fry until tender and slightly charred, about 5 minutes.
Add the yellow bell pepper strips to the pan and cook 2–3 minutes until tender, then transfer the vegetables to a plate and return the pan to the heat.
Add the remaining 1 tbsp butter and 1 tsp sesame oil to the pan over medium heat; add the coated chicken and cook, turning occasionally, until browned and cooked through, about 5–7 minutes; transfer the chicken to the plate with the vegetables.
In a small bowl, whisk together the chicken broth, honey, sugar, rice vinegar, 1/4 cup soy sauce, 1 tbsp sesame oil and a pinch of red pepper flakes (if using); set aside.
Return the pan to medium heat and sauté the minced garlic and minced ginger about 30 seconds until fragrant.
Pour the sauce into the pan (reserve about 2 tbsp) and bring to a simmer, cooking about 2–3 minutes to blend flavors.
Whisk the reserved ~2 tbsp sauce with the remaining 2 tbsp cornstarch until smooth, then pour into the simmering sauce and stir until the sauce thickens.
Return the chicken and vegetables to the pan and toss to coat evenly in the sauce; sprinkle with sesame seeds and serve hot.