Heat the olive oil in a skillet over medium heat.

Cook the onion for 4 to 5 minutes until softened.

Add the garlic and ginger and cook for 30 seconds.

Stir in the tomato paste, garam masala, curry powder, cumin, paprika, turmeric, chili powder, salt, and black pepper. Cook for 1 minute until fragrant.

Transfer the onion mixture to the crockpot.

Add the chicken pieces.

Pour in the tomato sauce and crushed tomatoes. Stir well to coat the chicken.

Cover and cook on Low for 5 to 6 hours or High for 2½ to 3 hours, until the chicken is tender.

Turn the slow cooker to Warm.

Stir together the heavy cream and Greek yogurt, then gently mix them into the sauce.

Let the curry sit for 10 minutes before serving.

Garnish with fresh cilantro and serve over basmati rice with warm naan.