In a bowl, whisk together orange zest, orange juice, brown sugar, rice vinegar, tamari, sriracha, ginger, garlic powder, and dissolved cornstarch until smooth.
Pat the chicken dry with paper towels and cut into bite-sized pieces.
Heat oil in a large nonstick skillet over high heat. Add chicken and kosher salt. Cook, stirring frequently, until just cooked through, about 3–4 minutes. Transfer chicken to a bowl and cover to keep warm.
In the same skillet, add the orange sauce. Cook over medium heat, stirring constantly, until thickened, about 30 seconds.
Return the chicken and any juices to the pan. Toss until evenly coated in the sauce.
Serve immediately over cooked rice and garnish with sliced scallions. Add extra sriracha if desired.