In a large bowl, mix Greek yogurt, lemon juice, ginger-garlic paste, turmeric, garam masala, cumin, coriander, smoked paprika, chili powder, and salt until well blended. Cut chicken breast into bite-sized pieces and coat thoroughly in the marinade. Cover and refrigerate for at least 30 minutes, but overnight is preferable for deeper flavor.

Heat a large pot over medium heat and add a splash of oil. Once hot, add marinated chicken in batches, ensuring not to overcrowd the pot. Sear for about 4-5 minutes until the chicken is browned on the outside but not fully cooked through. Remove the chicken and set aside while leaving the flavored juices in the pot.

In the same pot, add butter or ghee and melt over medium heat. Once melted, add chopped onions, sautéing for 5-7 minutes until they turn golden brown. Then, stir in minced garlic and grated ginger, cooking for an additional 1-2 minutes until fragrant.

Add the remaining spices—cumin, coriander, garam masala, and chili powder—along with crushed tomatoes. Stir and cook for about 10 minutes, stirring occasionally, until it thickens.

Return the seared chicken to the pot, pouring in heavy cream. Stir to combine, then reduce the heat to low. Let it simmer gently for about 15 minutes until the chicken cooks through.

Before serving, taste the sauce and adjust seasoning as needed. Garnish with fresh cilantro and serve.