Place Onion, Raisins, Garlic, Sesame Seeds, Chipotle Pepper, Peanut Butter And Crushed Tomatoes In Slow Cooker. Stir In Sugar, Cinnamon, Chili Powder, Cumin, Coriander, Nutmeg, And Cocoa Powder. Place Chicken In The Sauce. Cover; Cook On Low Until Chicken Is Very Tender, About 5 Hours.