Pat chicken thighs completely dry with paper towels. Season both sides generously with salt and pepper. Set aside.
In a small bowl, combine cumin, coriander, turmeric, paprika, cinnamon, cayenne, and crushed saffron threads. Mix well and set aside.
Heat olive oil in a large Dutch oven or tagine pot over medium-high heat until shimmering but not smoking.
Place chicken thighs skin-side down in the hot oil. Cook without moving for 5-6 minutes until deep golden brown. Flip and brown the other side for 3-4 minutes. Remove chicken to a plate and reduce heat to medium.
Add sliced onions to the same pot, scraping up browned bits. Cook until softened and translucent, 6-8 minutes. Stir in garlic and ginger, cooking for 1 minute until fragrant.
Sprinkle spice mixture over onions, stirring constantly for 30 seconds to toast spices. Pour in chicken broth, scraping the bottom to release flavorful bits.
Return chicken thighs to the pot, nestling them into the liquid. Add preserved lemon slices and green olives around the chicken. Liquid should come halfway up the chicken pieces.
Bring to a gentle simmer, then reduce heat to low. Cover tightly and cook for 35-40 minutes until chicken reaches 165°F internally and becomes fork-tender.
Remove the lid and increase heat to medium-high. Let sauce reduce for 5-7 minutes until it thickens slightly and coats the back of a spoon. Taste and adjust seasoning.
Garnish with fresh parsley and cilantro just before serving. Serve hot over couscous or with Moroccan bread.