In a bowl, combine the chicken, 1 teaspoon salt, garlic powder, paprika, ½ teaspoon curry powder, and Greek yogurt. Mix so each piece is coated. Let sit at least 30 minutes at room temperature or up to 4 hours in the fridge.

Heat the vegetable oil in a large skillet over medium heat. Add the marinated chicken in a single layer. Brown the pieces, stirring occasionally, until cooked through (about 6–8 minutes depending on size). Remove chicken and set aside.

In the same skillet, melt 2 tablespoons of butter over medium heat. Add minced garlic and diced onion. Cook, stirring, until the onion is translucent and soft (about 4–5 minutes).

Pour the tomato sauce into the pan. Stir in the sugar, 1 teaspoon salt, black pepper, and cayenne if using. Bring to a gentle simmer and let the flavors meld for 2–3 minutes.

Reduce heat to low. Add the heavy cream, garam masala, and the remaining ½ teaspoon curry powder. Stir until smooth. Simmer gently for 5–10 minutes until the sauce thickens slightly. Taste and adjust seasoning.

Stir in the remaining tablespoon of butter until melted. Return the cooked chicken to the skillet. Stir to coat every piece in the sauce and heat through for 2–3 minutes.

Sprinkle with chopped parsley if desired. Serve hot with warm naan or steamed rice.