Combine chicken pieces with salt, garlic powder, sweet paprika, curry powder, and Greek yogurt. Toss until evenly coated. Cover and refrigerate for at least 15 minutes.

Heat 2 tablespoons vegetable oil and 1 tablespoon butter in a large skillet over medium heat. Add minced garlic and diced onion. Sauté until the onion is soft and translucent, about 4 to 5 minutes.

Pour in the tomato sauce. Stir in sugar, salt, black pepper, heavy cream, and cayenne pepper if using. Add garam masala and curry powder. Bring to a gentle simmer and cook for 3 to 4 minutes.

While the sauce simmers, warm a second skillet over medium-high heat and add the remaining vegetable oil. Add the marinated chicken in single layers. Cook until browned and cooked through, about 5 to 7 minutes.

Transfer the cooked chicken into the sauce. Stir in the remaining butter until melted and incorporated. Simmer for 2 to 3 minutes, then taste and adjust seasoning.

Garnish with parsley if desired. Serve hot over steamed rice with warm naan.