First start by marinating the chicken. Season both sides of the chicken pieces with salt and pepper.
Before adding your other seasoning to the marinade, reserve the whole lemon and 1/2 tablespoon of the za'atar seasoning. After doing this, mix the remaining spices, oil, and garlic together in a small bowl. Pour the seasoning mix over the chicken. Add the sliced lemon, and onions to the marinade. Cover the chicken and let the chicken marinate in the refrigerator for at least four hours (the longer you marinade the chicken the better.)
When ready to cook the chicken, remove the chicken from the marinade bag or container, and season both sides of the chicken with salt, pepper, and the reserved 1/2 tablespoon of za'tar seasoning. Let the chicken rest and come to room temperature while you heat the pan up.
Heat a pan using medium high heat. Once the pan is hot, add a few drizzles of oil to the pan.
Add the chicken to the pan. Brown the chicken for two minutes on each side. Then turn heat down slightly to medium heat.
Cook the chicken for about eight to ten minutes or until the internal temperature of the chicken reaches 165 degrees. Make sure to flip the chicken halfway through the cooking time.
Remove the cooked chicken from the pan and let the chicken rest for a few minutes so that the chicken stays moist.
While the chicken is resting, cut the second lemon in half and squeeze the lemons over the chicken for more lemon flavor if you like.