Preheat the oven to 400 F (200 C).
In a bowl, mix the chicken with the onions, garlic, olive oil, spices with 2 tablespoons zaatar, lemon, stock, salt and pepper. (If you have time, leave in the fridge to marinate for a few hours or overnight).
Transfer the chicken and its marinade to a baking sheet large enough to accomodate all the chicken pieces lying flat and spaced well apart. They should be skin side up.
Sprinkle 1 tbsp zaatar over the chicken and put the pan into the oven. Roast for 40 to 50 minutes, until the chicken is browned and just cooked through. (Juices should run clear when thighs are pierced. If using a temperature guage, chciken is done when it reads 165F).
Transfer the hot chicken and onions to a serving plate and finish with a drizzle of olive oil and squeeze the juice of the caramelized lemons on to the chicken for added flavor.