In a medium bowl, combine sugar, 1/4 cup gluten free soy sauce, 2 1/2 tablespoons rice vinegar, and chicken broth. Set aside.
In a separate bowl, combine chicken pieces, 1 tablespoon gluten free soy sauce, and 1 teaspoon of vinegar. Marinate chicken for at least 30 minutes. Once the chicken has marinated, add egg whites and cornstarch, stirring until well-blended.
In your wok or large skillet, heat half of the oil over med-high heat. Add broccoli or bok choy to heated pan and stir fry until crisp tender. Remove vegetables from pan and set aside.
Heat remaining oil in skillet. Cook chicken in batches until golden on both sides- this will take 3-5 minutes. Remove chicken from wok with a slotted spoon and drain on paper towels. Tent with foil to keep chicken warm. If you have more than a couple tablespoons of oil left in the wok, discard the remaining oil (leave just a few tablespoons in the wok). Reduce the heat to med.
Cook the garlic and pepper flakes for about a minute. Add set aside soy sauce mixture. Increase heat to med-high and cook sauce for about 15 minutes. Stir two teaspoonfuls of cornstarch into a little water and whisk it into the sauce. Once the sauce is thickened and bubbly, add the chicken, vegetables and sesame seeds. Stir around until everything is well coated with the sauce and heated through. Top with thinly sliced green onions and serve over jasmine rice.
Freezing Directions: When vegetables and chicken are done cooking, allow to cool. Once the sauce is thickened and bubbly, add chicken, vegetables and sesame seeds. Allow to cool. Place cooled mixture into freezer bags, removing as much air as possible. Seal, label and freeze.
To serve: Thaw and heat through. Top with thinly sliced green onions and serve over jasmine rice with a vegetable or salad.