Mix all marinade ingredients together thoroughly in a small bowl. Pour half of marinade over raw chicken in a container with a lid. Cover and refrigerate until ready to use. Reserve other half of marinade for basting later in the cooking process.
In a large skillet, heat oil over medium high heat. Carefully add chicken to heated oil. Use a slotted spoon to avoid adding the marinade to the hot oil. Add the garlic and ginger from the marinade, then dispose of the leftover marinade from the chicken.
Stir fry until chicken is cooked through; remove chicken from skillet and keep warm. Add the red bell pepper slices to the skillet and stir fry for 2 minutes. Next, add cornstarch to the reserved marinade. Add cornstarch/marinade mixture and the chicken to the peppers in the skillet; stir fry for 2 more minutes.
Remove skillet from heat. Season with salt and pepper; garnish with scallions and cashews. Serve over rice.
You'll need to plan ahead for this recipe to ensure you allow time for the chicken to marinate.