Prepare the Chicken:
Thinly slice the chicken breasts (freezing for 20 minutes beforehand makes slicing easier).
Coat the chicken evenly in cornstarch and shake off any excess.
Cook the Chicken:
Heat vegetable oil in a large skillet or wok over medium-high heat.
Add the chicken in batches, ensuring the pan isn’t overcrowded. Cook for 3–4 minutes per side until golden and crispy. Remove and set aside.
Make the Sauce:
In the same pan, add garlic and ginger, stirring for 30 seconds until fragrant.
Pour in soy sauce, brown sugar, sesame oil, and water. Stir and bring the sauce to a gentle simmer.
Combine:
Add the cooked chicken back into the skillet, tossing to coat the pieces evenly in the sauce.
Stir in sliced green onions and cook for another minute.
Serve:
Serve the Mongolian Chicken over steamed rice, zucchini noodles, or chow mein.