Set slow cooker to low heat for six hours. Place your olive oil and chicken thighs in the slow cooker. Sprinkle with the shawarma spice and salt and cook.
After six hours, allow the chicken to cool and then pull apart into bite-sized pieces. Place in the freezer for later, or for immediate use go to the next step.
If putting in the freezer, add a few spoonfuls of the cooking liquid to your storage container with the chicken - this will help it stay moist when reheated, though it's not necessary if you're putting it under the broiler immediately.
Oven:
Defrost the shawarma overnight. If cold from the fridge - place on a foil lined baking sheet into a 350°F (175°C) oven for 10 minutes. Once warmed, move the chicken closer to the broiler, then broil for an additional 5-10 minutes until slightly charred and crispy.