Heat oven to 350° F.
Measure all spices for Spice Mix into a small bowl. Stir together. Set aside.
Heat oil in an 6-8–qt. Dutch oven over medium-high heat. Season chicken with salt and pepper; add to pot and cook, turning, until browned, 10 to 15 minutes. Transfer chicken to a plate. (It will not be cooked through at this point, it gets cooked the rest of the way in the oven)
Add onions to the hot oil in the pot; cook until golden, 10 to 12 minutes.
Add Spice Mix; cook for 2 minutes.
Return chicken to pot with stock; boil.
Bake chicken, covered, until tender and fully cooked, 30 to 35 minutes.
Stir in olives, butter, parsley, lemon (if using), and cilantro into pot, and cook for 6 minutes. Serve with crusty bread, couscous, or pasta.