Add the chicken thighs to the slow cooker.
Add the onion, garlic, and ginger. Stir to combine.
Add the garam masala, cumin, coriander, turmeric, cayenne pepper, cardamom, and black pepper. Stir to combine.
Add the tomato paste, chicken broth, coconut milk, and honey. Stir to combine.
Cover and cook on low for 6-8 hours or on high for 3-4 hours.
Once the chicken is cooked through, stir in the cilantro and season with salt to taste.
Serve over basmati rice or with naan bread.