Heat 1 tablespoon of oil in a large skillet or wok over medium-high heat.
Add minced garlic and stir-fry for about 30 seconds until fragrant.
Add sliced chicken breast and cook until browned and cooked through, about 5-7 minutes.
Push the chicken to one side of the skillet. Add another tablespoon of oil if needed, then add the mixed vegetables.
Stir-fry the vegetables until tender-crisp, about 3-4 minutes.
Combine the chicken and vegetables in the skillet.
Add soy sauce, oyster sauce, sesame oil, salt, and pepper. Stir-fry for another 1-2 minutes until everything is well coated and heated through.
Serve hot over cooked rice or noodles.