In a large zip-top bag, combine cumin, cinnamon, 3/4 teaspoon salt, and 1/2 teaspoon pepper; add chicken and toss to coat. In a large skillet, heat oil over medium-high. Cook chicken, skin side down, until golden, about 4 minutes; flip and cook 2 minutes.
In a 5-to-6-quart slow cooker, place onion, garlic, and ginger. Add chicken, skin side up, then top with tomatoes and their liquid and raisins. Cover and cook on high until chicken is tender, 3 1/2 hours (or 6 hours on low).