To a medium mixing bowl, stir together the Greek yogurt, lemon juice, minced garlic, and seasonings.
Add the chicken thighs to a large zip top bag pour the yogurt mixture on top. Seal the bag and massage the marinade into the chicken so it is fully coated. Move to the fridge for at least 4 hours, up to overnight.
Once marinated, add the sliced onion to the bottom of a 6 quart slow cooker and pour the chicken on top.
Cover and cook on LOW for 4-6 hours or HIGH for 3-4 hours.
Once the chicken is fully cooked, remove from the crockpot, slice into strips, and place back in the sauce for serving.
To a small mixing bowl, whisk together the plain Greek yogurt, minced garlic, grated cucumber, lemon juice, and seasonings.
Serve as a bowl over yellow rice with toppings or lay out a slice of pita bread, spread some yogurt sauce down the middle then pile in some sliced chicken. Top with sliced tomatoes, Arabic pickles, lettuce, etc.
