Prep your chicken and add it to a large ZipLoc bag along with the cornstarch. Toss until coated.
Add the sauce ingredients (brown sugar, garlic, ginger, soy sauce, sriracha, and water) to a small bowl and whisk together.
Add the oil to a skillet, along with the chicken. Give it a stir and cook it over medium-high heat for a few minutes, stirring occasionally, until the chicken is no longer pink on the outside.
Pour the sauce into the skillet and reduce the heat to medium. Cook for a few more minutes until the chicken is cooked through and the sauce has thickened.
Serve with rice and garnish with scallions if you wish.
Notes
The ginger is much easier to grate if it's frozen. I always keep some fresh ginger in the freezer and I use my Microplane grater/zester to easily grate it.