Pound the chicken to an even thickness and place in a zip close bag.
In a bowl combine the soy sauce, pineapple juice, rice vinegar, 1 tsp sesame oil, ground ginger, garlic powder and Sriracha (if using). Reserve 1/2 cup of the sauce in a small container and set aside for later use. Pour the remaining sauce in the bag with the chicken and place in fridge for at least 2 hours, up to 24 hours.
Heat grill to medium and remove chicken from marinade (discard marinade). Grill chicken for 3 to 4 minutes per side, until chicken reaches 160 degrees internally. Remove from grill to a plate and cover loosely with tinfoil.
Place the reserved sauce in a small saucepan and bring to a low boil. In a small bowl combine 1 tablespoon of water with the 1 tsp of cornstarch, then pour into the saucepan. Stir and let simmer until the sauce thickens. Brush the thickened sauce over the cooked chicken and sprinkle with sesame seeds for garnish.
For the Stir-Fry Veggies:
Heat a large wok over medium heat and add the olive oil and sesame oil. Once hot, toss in the broccoli and stir for about 1 minute. Add the bell pepper, onion and garlic to the wok, stirring occasionally for about 2 to 3 minutes. Once the veggies are all crisp-tender, remove from heat.
Serve the chicken over a bed of white rice along with the stir-fry veggies! Enjoy!