Prep onion, garlic and mushrooms as noted. Chop kale and set aside.
Place arrowroot starch on a plate or shallow bowl and add salt and pepper. Mix with a whisk.
Dredge the chicken thighs in the starch mixture so they are lightly coated on all sides. Set aside on a plate.
Heat a large skillet over medium heat and add about 2 tbsp avocado oil. Once hot, add the thighs to the pan to cook (you may need to do this in batches depending on the size of your skillet).
Cook the chicken without disturbing, for about 5-6 minutes per side, or until golden brown but not burnt. If you are cooking in batches, you may need to add more avocado oil in between batches. Once both sides are cooked, remove and place on a plate.
While the chicken is cooking, prep the sauce by adding the sauce ingredients to a bowl or measuring glass and mixing.
When the chicken is done, keep the skillet at medium heat and add 1 tbsp avocado oil. Add the onion, garlic, and mushrooms. Saute until mushrooms start to soften, about 2-3 minutes.
Add the sauce. Scrape the skillet to deglaze. Stir and reduce heat to low to simmer.
Add in the chopped kale and mix it in with the sauce.
Nestle the chicken back into the sauce and kale mixture and let simmer for 5-6 minutes, or until the sauce thickens and the chicken is completely cooked through.