In a medium bowl, combine chicken thighs with salt, garlic powder, sweet paprika, and curry powder, ensuring each piece is well coated. Add Greek yogurt and mix until evenly distributed. Cover and let marinate for at least 15 minutes at room temperature.

Heat vegetable oil in a large skillet over medium-high heat until shimmering. Add the marinated chicken thighs, cooking for about 8 to 10 minutes until golden-brown on both sides. Remove from skillet and keep warm.

Lower the heat to medium and add butter to the skillet. Once melted and foamy, add minced garlic and diced onion, sautéing for about 3-4 minutes until the onion is translucent.

Stir in the tomato sauce and a sprinkle of sugar. Allow to simmer for 2-3 minutes until thickened. Return the cooked chicken thighs to the skillet, then pour in the heavy cream, stirring until well incorporated.

Sprinkle in cayenne pepper (if desired) and garam masala, along with black pepper to taste. Reduce heat to low and let simmer for 10 minutes, stirring occasionally.

Stir in remaining butter until melted and fully combined. Remove from heat and let rest for a minute. Serve hot, garnished with fresh parsley, alongside warm naan and fluffy rice.