1 1/2 pounds boneless, skinless chicken breast, cut into 1-inch cubes
1 tablespoon cornstarch
Coarse salt and ground pepper
2 tablespoons vegetable oil, such as safflower
6 cloves garlic, minced
8 scallions, white and green parts separated, each cut into 1-inch pieces
2 tablespoons rice vinegar
3 tablespoons hoisin sauce
3/4 cup raw cashews (4 ounces), toasted
White rice, for serving (optional)
In a medium bowl, toss chicken with cornstarch until chicken is coated; season with 3/4 teaspoon salt and 1/4 teaspoon pepper.
In a large nonstick skillet, heat 1 tablespoon oil over medium-high heat. Cook half the chicken, tossing often, until browned, about 3 minutes. Transfer to a plate.
Add remaining oil and chicken to skillet along with the garlic and white parts of scallions. Cook, tossing often, until chicken is browned, about 3 minutes. Return first batch of chicken to pan. Add vinegar; cook until evaporated, about 30 seconds.
Add hoisin sauce and 1/4 cup water; cook, tossing, until chicken is cooked through, about 1 minute. Remove from heat. Stir in scallion greens and cashews. Serve immediately over white rice, if desired.