Cut the chicken breast into 2-inch chunks and add to a large bowl.
Season chicken with salt and lemon juice, then mix until well-coated.
Add yogurt, minced garlic, kashmiri red chili powder, onion powder, powdered ginger, garam masala, cumin, paprika, turmeric, and ground coriander to the chicken. Stir until marinade is well-combined and chicken is coated.
Cover with plastic wrap and marinate in the fridge overnight.
The next day, pour the tomato puree into the slow cooker. Add the marinated chicken, then cover and cook on LOW for 6 hours.
After 6 hours, turn off the slow cooker. Stir in heavy cream, tomato paste, butter, and powdered fenugreek until well-combined.
Optionally garnish with fresh cilantro and serve hot with basmati rice and naan.