Make the sauce. In a medium bowl, whisk soy sauce, brown sugar, 2 tablespoons water, vinegar, sesame oil, ginger, garlic, cornstarch, and sriracha.
Add broccoli to a medium, microwave safe bowl and add remaining water. Cover with plastic wrap and microwave on high until lightly steamed, 2 minutes. Carefully remove plastic.
Heat oil in a large skillet over medium high heat. Add chicken and cook until browned on all sides and cooked to an internal temperature of 165°F, tossing frequently, 7-8 minutes total. Add sauce and cook until reduced and thickened, 2 minutes.
Divide rice between four bowls, then divide chicken and broccoli between bowls. Top with scallions and sesame seeds and serve immediately.
Notes
Storage: Store any leftovers in an airtight container in the fridge for up to 4 days. It's best to store the chicken and rice separately to reheat.