Remove any unwanted fat from the chicken and cut the chicken into small uniform pieces.
To the slow cooker, add the chopped chicken, tomatoes, onion, garlic, ginger, lemon juice, garam masala, chili powder, cumin, fenugreek, cayenne pepper, and bay leaf.
Secure the lid, set to high and cook for 3-4 hours, or until the chicken is cooked through.
Before serving add half and half and yogurt, stir to combine and let cook for about 5 minutes longer, until the sauce is warmed through.
Garnish with cilantro and serve over rice.