Trim the chicken breasts and cut into pieces at least 1 inch square.
Combine soy sauce, rice vinegar, sesame oil, and garlic powder.
Put the chicken into a Ziploc bag and pour in half the marinade. Let chicken marinate in the fridge for at least 4 hours.
Preheat the oven to 425F/220C and cover a large baking sheet with foil.
Drain the marinated chicken well in a colander.
Spread the chicken on the hot baking sheet and cook for 8 minutes.
While the chicken cooks, trim the ends of the sugar snap peas and slice the red bell peppers.
Toss the veggies with the peanut oil.
Arrange the vegetables around the chicken after 8 minutes and cook for another 12 minutes.
Brush cooked chicken and vegetables with remaining marinade and sprinkle with black sesame seeds.
