In a medium bowl, whisk together soy sauce, honey, rice vinegar, sesame oil, garlic, ginger, black pepper, and red pepper flakes (if using). Add the chicken thighs and marinate for at least 30 minutes, or up to 2 hours in the refrigerator for more flavor.

Preheat a large skillet or grill pan over medium-high heat. Remove chicken from the marinade, reserving the marinade for later. Cook the chicken for about 5-7 minutes on each side, or until fully cooked and no longer pink in the center. Remove from the skillet and let rest for a few minutes before slicing.

In the same skillet, add the broccoli and bell peppers. Stir-fry for about 5 minutes, or until the vegetables are tender-crisp.

While the vegetables are cooking, pour the reserved marinade into a small saucepan and bring to a boil. Reduce heat and simmer for about 5 minutes, or until slightly thickened.

To serve, divide the cooked jasmine rice among bowls. Top with sliced chicken, stir-fried vegetables, and drizzle with the thickened marinade. Garnish with chopped green onions and sesame seeds.