Easy Green Curry Chicken

Name: Easy Green Curry Chicken
Prep time: 30 min
Cook time: 20 min
Total time: 50 min
Cuisine: Thai
Ingredients: 1½ pounds boneless skinless chicken thighs or breast ((thinly sliced)); 1 tablespoon cornstarch; 1 tablespoon water; 2 teaspoons oyster sauce; 3 tablespoons neutral oil ((such as canola, vegetable, or avocado oil, divided)); 1 medium onion ((thinly sliced)); 4 ounces green curry paste ((or 2 ounces for milder curry)); 5 cups mixed vegetables; 13.5 ounces coconut milk ((1 can—about 1 2/3 cups)); 1¼ cup chicken stock; 1 tablespoon sugar; 1 tablespoon fish sauce; ½ cup basil leaves ((Thai basil or sweet basil)); steamed jasmine rice ((to serve))