Place a large pan on the stove and turn the heat to medium-high.
Add 1 tablespoon oil and let it heat for 30 seconds.
Put the chicken in the pan and spread it out in one layer.
Cook for 5–7 minutes, stirring often, until the chicken is no longer pink.
Remove the chicken from the pan and set it on a plate.
Pour the remaining oil into the pan.
Add the frozen vegetables and cook for 4–5 minutes, stirring until hot.
Stir in the garlic and cook for 30 seconds.
Mix cornstarch and water in a small bowl, then pour it into the pan with the soy sauce.
Return the chicken to the pan and stir for 2–3 minutes until the sauce thickens.
Serve over warm rice.