Place the chicken pieces, onion, garlic, and ginger into the slow cooker.
In a bowl, stir together the tomato sauce, yogurt, garam masala, cumin, paprika, turmeric, salt, and pepper until smooth.
Pour the sauce mixture over the chicken and stir to coat everything evenly.
Cover and cook on low for 6 hours or on high for 3 hours until the chicken is tender.
Stir in the heavy cream during the last 15 minutes of cooking.
Spoon the cooked basmati rice into bowls and top with the chicken tikka masala.
Sprinkle with chopped cilantro before serving.