Place the chicken and ¼ cup cornstarch in a resealable plastic bag, shake to coat evenly.
Heat the vegetable oil in a large pan over high heat
Add the chicken to the pan in a single layer and season to taste with salt and pepper (keeping in mind the sauce has plenty of salt in it!).
Cook for 3-4 minutes per side or until browned. Cook in multiple batches if needed.
Remove the chicken from the pan and place on a plate lined with paper towels
Add the garlic and ginger to the pan and cook for 30 seconds. Add the soy sauce, sesame oil, water and brown sugar to the pan and bring to a simmer.
Mix the 2 teaspoons of cornstarch with 1 tablespoon of cold water. Add the cornstarch to the sauce and bring to a boil; boil for 30-60 seconds until just thickened.
Add the chicken and green onions to the pan and toss to coat with the sauce. Serve over rice if desired.