In a large bowl, combine Greek yogurt, lemon juice, ginger-garlic paste, turmeric, garam masala, cumin, coriander, smoked paprika, chili powder, salt, and oil. Cut the chicken into bite-sized pieces and coat thoroughly with the marinade. Cover and refrigerate for at least 1 hour or overnight.

Heat a grill pan over medium-high heat. Sear the marinated chicken for 4-5 minutes on each side until cooked through and slightly charred, or bake at 400°F for 15-20 minutes. Set aside.

In a deep skillet, melt butter or ghee over medium heat. Add chopped onions and sauté for 5-7 minutes until golden. Stir in minced garlic and grated ginger for an additional minute.

Sprinkle in turmeric, garam masala, cumin, coriander, and smoked paprika, stirring continuously for another minute. Mix in tomato paste and crushed tomatoes, and simmer for 10 minutes until thickened.

Gradually stir in heavy cream or coconut milk over low heat, and let it simmer for another 5 minutes. Adjust seasoning with sugar if needed.

Fold in the cooked chicken and simmer for 5 minutes, adding a splash of lemon juice. Garnish with cilantro and serve warm with basmati rice or naan.