Rinse the chicken and pat it dry. Cut the chicken into 2-inch pieces. Heat the oil in a large skillet and cook the chicken over medium heat for 8 minutes, or until it is opaque. Add the bell pepper, green onions, garlic, and mushrooms. Stir-fry for 3 to 4 minutes. In a small bowl, whisk together the maple syrup, soy sauce, sherry, cornstarch, ginger, and cayenne until the cornstarch dissolves. Pour over the chicken and vegetables and cook for 3 minutes, stirring until sauce thickens and develops a glaze. Stir in the cashews and heat for 1 minute more. Serve over rice.