In a bowl, add the chicken, soy sauce, garlic powder, onion powder, ginger, brown sugar, rice vinegar, and olive oil. Combine and coat each piece well with the marinade. Cover the bowl and let the chicken marinate in the fridge for 30 minutes.
Heat 1 tablespoon oil in a large skillet or large frying pan over medium heat. Remove the chicken from the marinade and shake off any excess liquid. Cook for 5-7 minutes per side until golden brown and fully cooked (165°F internal temperature, checked with an instant-read thermometer). Remove the chicken pieces from the pan and let them rest.
In a small bowl, mix soy sauce, olive oil, brown sugar, garlic powder, ginger, sesame oil, and rice vinegar. In another bowl, mix cornstarch and water until smooth. Stir and cook the sauce for 1 minute, then add the cornstarch mixture. Cook until the sauce thickens (1-2 minutes, or until it coats the back of a spoon).
If the sauce is too thick, thin it with water. Add 1 tablespoon at a time, stirring until desired consistency is reached. Adjust to taste.
Heat 2 teaspoons of sesame oil in a hot pan, then add minced garlic, broccoli, carrots, and red bell pepper. Cook for 2-3 minutes. Add 2 tablespoons water, cover, and steam them for 2 minutes until they become tender.
To assemble the chicken teriyaki bowls, slice the cooked chicken. Divide the cups of rice into bowls, then top the rice with sliced chicken and veggies. Pour teriyaki sauce over the top and garnish with sesame seeds or green onions.