Trim and cut the chicken breasts into roughly 1-inch pieces.
Whisk together soy sauce, rice vinegar, your chosen sweetener (such as Golden Monkfruit), sesame oil, and garlic powder to make the marinade.
Place the chicken in a zip-top bag or shallow container and add half the marinade. Seal and refrigerate for at least 4 hours or up to all day.
Preheat the oven to 425°F (220°C). Line a large baking sheet with foil and place it in the oven to heat while the oven comes to temperature.
Drain the marinated chicken in a colander, discarding excess marinade.
Carefully remove the hot baking sheet from the oven and arrange the chicken pieces in a single layer with space between them; return to the oven and bake 8 minutes.
While the chicken bakes, trim the snap peas and cut the bell peppers into strips similar in thickness to the peas. Toss the vegetables in the peanut oil in a bowl.
Remove the pan from the oven after 8 minutes and arrange the oiled vegetables around the chicken so they contact the pan; return to the oven and bake about 12 minutes more, until chicken is cooked through and lightly browned.
Brush the cooked chicken and vegetables with the remaining marinade, sprinkle with sesame seeds, and serve hot.