In a small bowl, mix together the ingredients for the spice mix then place chicken thighs into a large bowl and pour spice mix on top and rub the chicken throughout to get the spices incorporated. Refrigerate for 3-4 hours.
Heat 2-3 tablespoons of olive oil in a large cast iron skillet over medium-high heat. Add chicken and brown on both sides. Remove and place on plate. It's okay if it's not fully cooked through yet. You are just browning it.
Add the onions and cook for 10-15 minutes, until softened and brown. Add cinnamon stick to the onions then place the chicken back on top.
Sprinkle olives all over, along with the preserved lemons. Pour the preserved lemon juice and chicken stock together and mix then pour into skillet.
Cover and let simmer on low heat for 30 minutes.
Prior to serving, sprinkle fresh parsley on top, if desired.