In a skillet, heat olive oil and sauté onion, garlic, and ginger until fragrant.
Add garam masala, cumin, turmeric, paprika, and cayenne pepper; cook for 1 minute.
Transfer the mixture to a slow cooker. Add chicken, coconut milk, tomato paste, salt, and pepper.
Stir to combine and set the slow cooker to low for 6-7 hours or high for 3-4 hours.
Serve hot, garnished with fresh cilantro. Pair with steamed rice or naan.