Cut the chicken into bite-sized pieces and season lightly with black pepper.
Heat vegetable oil in a wok or large skillet over medium-high heat.
Cook the chicken for 5–6 minutes until golden and fully cooked. Remove and set aside.
Stir-fry the sliced bell peppers and minced garlic for 2–3 minutes until slightly tender but still crisp.
Return the chicken to the pan and add soy sauce, chili garlic sauce, and a pinch of red chili flakes.
Toss everything together for 2–3 minutes until the chicken and vegetables are evenly coated with the spicy sauce.
Serve hot with steamed rice or noodles, garnished with sliced green onions if desired.