Place chicken, onion and garlic inside a slow cooker sprayed with nonstick cooking spray.
In a bowl, whisk together chicken stock, tomato paste, curry powder, ginger, garam masala, turmeric, salt, and pepper. Pour over chicken then stir to combine and coat chicken. Cover and cook on low for 6 hours.
After cooking, stir in yogurt, lime juice and brown sugar until well combined.
Garnish with fresh cilantro and serve over rice, if desired.
*Rice not included in nutrition information.