In a large bowl, mix Greek yogurt, lemon juice, ginger-garlic paste, turmeric, garam masala, cumin, coriander, smoked paprika, chili powder, salt, and a splash of oil. Cut the chicken breasts into bite-sized chunks and coat them evenly. Cover and refrigerate for at least 1 hour, preferably overnight.

Preheat a skillet over medium-high heat. Add oil and sear the marinated chicken chunks for 4-5 minutes on each side until cooked through. Alternatively, bake chicken at 400°F for 15-20 minutes.

In the same skillet, melt butter or ghee over medium heat. Add chopped onions and sauté until golden brown, about 5-7 minutes. Stir in minced garlic and ginger, cooking for an additional minute.

Once the onions are caramelized, sprinkle in the remaining spices and stir for a minute. Add tomato paste and crushed tomatoes, stirring well. Simmer on low heat for 10 minutes.

Reduce heat and stir in heavy cream or coconut milk. Season with salt and sugar, simmer gently for 5-7 minutes.

Add the seared chicken back into the sauce, stirring to coat. Allow to simmer together for an additional 5 minutes.

Serve hot over basmati rice or naan, garnished with lemon juice and cilantro.