Add the chicken pieces, cauliflower florets, onion, garlic, and ginger to the slow cooker insert.
Pour in the crushed tomatoes and Greek yogurt.
Add the butter, garam masala, cumin, turmeric, paprika, and salt.
Stir everything until the chicken and cauliflower are evenly coated with the sauce and spices.
Cover and cook on low for 6 hours.
Stir gently before serving and sprinkle with fresh cilantro.