Combine chicken, onions, celery, carrots, olive oil, 1 tablespoon soy sauce and salt and pepper together and put into the slow cooker. Cook on high for 2 -3 hours.
Remove the contents of the cooker and reserve any cooking juices that have accumulated on the bottom of the cooker.
Return the chicken mixture back to the cooker.
In a bowl, combine all the sauce ingredients and mix well.
In a smaller bowl, combine the Thickener ingredients (cornstarch and water). Mix until very well combined.
In a saucepan, combine the sauce and the cooking juices together. Stir well and heat to boiling. Add the thickener, slowly by the tablespoon and stir until it thickens.
Add the whole mixture to the cooker and stir to coat. Add the cup of cashews, stir and continue to cook for another 30 minutes.