Dice the boneless skinless chicken thighs into 1-inch pieces, then combine with Greek yogurt, lemon juice, ginger, garlic, chili powder, garam masala, turmeric, and salt in a bowl. Coat well and refrigerate for at least 1 hour, preferably overnight.

Heat oil in a large sauté pan over medium-high heat. Add marinated chicken pieces without overcrowding and cook for 5-6 minutes until opaque. Remove and set aside.

In the same pan, sauté diced onion for 3-4 minutes until translucent. Add ginger, garlic, chili powder, garam masala, coriander, and cumin. Cook for another minute.

Stir in cashews, crushed tomatoes, coconut sugar, and water. Mix well and simmer for about 5 minutes.

Transfer sauce to a blender and blend until smooth. Alternatively, use an immersion blender in the pan.

Return blended sauce to heat, stir in butter and cream until melted, then fold in cooked chicken. Simmer for 3-5 minutes.

Serve warm over basmati rice and garnish with cilantro.