Cut chicken into bite-sized pieces and place in a large mixing bowl.
Chop the red and green bell peppers, slice the onion, and mince the garlic. Add to the bowl with the chicken.
In a separate bowl, combine soy sauce, honey, sesame oil, rice vinegar, ground ginger, black pepper, and red pepper flakes. Whisk until well mixed.
Pour the sauce over the chicken and vegetables. Toss until evenly coated and spread on a baking sheet.
Bake in a preheated oven at 400°F for 25-30 minutes, stirring halfway through.
Garnish with sliced green onions before serving.