Pat chicken pieces dry with paper towels. In a medium heat bowl,toss chicken with cornstarch until coated; season generously with salt & pepper

In a large wok, heat 2 teaspoons oil over medium-high. Cook half the chicken,turning once until browned, but not completely cooked through, 2 to 3 minutes total. Then trasfer to a plate. Repeat the other half.

To wok, add remaining 2 teaspoons oil, onion, bell peppers, (chillies); cook over medium-high heat, tossing often, until beginning to brown, 3 minutes. Add garlic; cook until fragrant, about 1 minute.

Add 1/4 cup water, vinegar, soy sauce, oyster sauce, and chicken to wok; cook, tossing, until chicken is cooked through, about 1 minute. Remove from heat. Stir in basil leaves. Serve immediately, over white rice.