In a medium bowl, combine the Greek yogurt, lemon juice, cumin, garam masala, salt, ginger, and cubed chicken. Stir until well combined and the chicken is completely coated. Transfer to the fridge to marinate for 10 to 15 minutes.
Preheat a large skillet over medium-high heat. Add the marinated chicken and cook, stirring occasionally, until cooked through, about 5 to 7 minutes. Remove the chicken from the pan and set aside.
Wipe the skillet clean and return to medium-high heat. Add the butter or ghee and then add the onions. Sauté for 5 minutes or until the onions begin to soften.
Add the garlic, jalapeño, cumin, paprika, and garam masala. Toast for 1 to 2 minutes.
Add the tomato sauce, heavy cream, and salt. Bring to a simmer. Once it comes to a simmer, add the chicken back to the skillet and stir to combine. Remove from heat and serve hot over cooked rice. Garnish with freshly chopped cilantro (optional).
