Dissolve cornstarch in chicken broth in a bowl; stir in soy sauce, ginger, and hot sauce. Set aside.

Heat 1 tablespoon oil in a wok or large skillet over high heat. Add chicken; cook and stir until no longer pink, about 5 minutes. Transfer chicken to a plate; set aside.

Add remaining 1 tablespoon oil to the wok. Add onion, bell pepper, and water chestnuts; cook and stir until onion has softened and water chestnuts are hot, about 5 minutes. Stir reserved sauce to redistribute cornstarch; stir into the wok. Bring to a boil. Add reserved chicken; stir until sauce thickens and chicken is hot. Sprinkle with cashews.