In a small bowl, stir together 2 teaspoons of the cumin and 2 teaspoons salt. Set aside. Season the chicken on both sides with salt and pepper.
In a large Dutch oven over medium-high, heat 2 tablespoons of the butter. When the foaming subsides, add the onions and garlic and cook, stirring occasionally, until lightly browned, about 5 minutes. Add the remaining 3 teaspoons cumin, the turmeric, ginger and coriander. Cook, stirring constantly, until fragrant, about 30 seconds. Stir in 1½ cups water, scraping up any browned bits. Nestle the chicken in the liquid, turning to coat. Cover, reduce to medium-low and cook for 20 minutes, adjust the heat as needed to maintain a gentle simmer.
Using tongs, turn the chicken. Cover and continue to cook until tender, another 25 minutes. Using tongs, transfer the chicken to a plate. Bring the liquid in the pot to a simmer over medium-high and cook, stirring frequently, until the liquid is thickened, 10 to 14 minutes.
Return the chicken to the pot and stir, roughly breaking up the pieces. Off heat, add the remaining 3 tablespoons butter, stirring until melted, then stir in the olives and lemon zest and juice. Taste and season with salt and pepper. Transfer to a platter and serve with the cumin-salt mixture for sprinkling to taste.
