Marinate the chicken and onions for at least 30 minutes.
Roast the potatoes for 10 minutes.
Add the chicken and onions and bake for another 10 minutes.
Combine the leeks with lemon zest, olive oil, and salt.
Add the leeks on top of the potatoes and finish roasting for 15 more minutes.
Make and serve with the garlicky yogurt sauce & top with fresh parsley.