Season the chicken pieces with salt and pepper. Heat the vegetable oil in a large skillet, over medium high heat, until very hot. Working in batches, add the chicken and stir fry until golden brown, about 4-5 minutes. Transfer the chicken to a plate and reserve.
Add the bell peppers and garlic, and cook until crisp-tender, about 3 minutes.
While the veggies are cooking, make the sauce. In a bowl, mix the hoisin sauce, soy sauce rice vinegar, honey, grated ginger, red pepper flakes, sesame oil, water and corn starch until well combined. Reserve.
When the veggies are crisp-tender, add the chicken back into the pan and pour the reserved sauce over the chicken and veggies, tossing so everything is coated. Cook for a couple of minutes, until the sauce thickens.
Add the cashews and scallions and stir to combine.
Serve immediately or, if meal prepping, divide into 6 to 8 containers. It will keep in the fridge for 3-4 days.