Season chicken pieces with salt and pepper. Heat vegetable oil in a large skillet over medium-high heat and brown chicken on all sides, about 6-8 minutes total. Transfer to slow cooker.

In the same skillet, sauté chopped onion until translucent, about 5 minutes. Add minced garlic and grated ginger, cooking for another minute until fragrant.

Add all spices to the onion mixture and cook for 30 seconds until aromatic. Stir in tomato paste and cook for one additional minute.

Add drained diced tomatoes to the skillet and cook for 3-4 minutes, breaking them down slightly with a wooden spoon.

Pour the entire onion and tomato mixture into the slow cooker with the chicken. Add coconut milk and stir to combine all ingredients evenly.

Cover and cook on low for 6-7 hours or high for 3-4 hours, until chicken is extremely tender and flavors are well developed.

In a small bowl, whisk Greek yogurt until smooth. Gradually add 1/4 cup of the hot korma liquid to temper the yogurt, then stir this mixture back into the slow cooker.

Add heavy cream and stir gently. Taste and adjust seasoning with salt as needed.

Garnish with fresh cilantro and serve with a squeeze of lime juice over steamed basmati rice or warm naan bread.

Allow the korma to rest for 5 minutes before serving to let the sauce thicken slightly and flavors settle.