While most stir fry recipes use corn starch, that's not a keto-friendly solution. For a thick stir fry sauce that's keto approved, you can add a mixture of arrowroot powder and water at the end.   To use arrowroot to thicken the sauce, first combine 1 tablespoon of arrowroot powder with 1 tablespoon of water in a separate bowl. Remove the chicken stir fry from the heat and mix the arrowroot mixture into the sauce. Stir to combine.   Since most of the liquid cooks off, you likely won't need arrowroot for this recipe, but it's a great trick to keep handy for other keto recipes.