Start by adding the chicken pieces directly to the slow cooker. Spread them out so they cook evenly.
Sprinkle the diced onion garlic powder and ground ginger over the chicken. Give everything a gentle stir so the seasoning coats the meat.
In a medium bowl whisk together the coconut milk tomato sauce curry powder turmeric paprika salt black pepper and brown sugar. Take a moment to smell it. That is the good stuff.
Pour the sauce over the chicken and stir gently until everything is coated. Make sure the chicken is mostly submerged in the sauce.
Cover and cook on Low for 6 hours or High for 3 hours. The chicken should be tender and the sauce fragrant and golden.
In a small bowl whisk together the cornstarch and cold water until smooth. Stir this mixture into the slow cooker.
Turn the heat to High and cook uncovered for about 15 minutes until the sauce thickens slightly.
Serve the chicken and sauce over rice or with warm naan and finish with fresh cilantro if you like.