In a medium bowl, combine chicken, 1 teaspoon salt, garlic powder, sweet paprika, 1 teaspoon curry powder, and Greek yogurt. Toss until evenly coated; marinate at least 15 minutes (up to 4 hours refrigerated).

Heat vegetable oil in a large skillet over medium-high heat. Add the marinated chicken in a single layer and cook 8–10 minutes, stirring occasionally, until browned and cooked through. Transfer chicken to a plate; leave any browned bits in the pan.

Reduce heat to medium and add 1 tablespoon butter. Add minced garlic and diced onion with a pinch of salt; sauté 3–4 minutes until translucent and fragrant, scraping up browned bits.

Stir in tomato sauce and sugar; simmer 2–3 minutes to mellow the acidity.

Return chicken and any juices to the skillet. Lower heat and pour in heavy cream; stir gently until the sauce turns a uniform orange.

Season with cayenne (optional), garam masala, remaining 1/2 teaspoon curry powder, and black pepper. Simmer on low 10 minutes, stirring occasionally; adjust salt to taste.

Turn off heat and stir in remaining 2 tablespoons cold butter until melted and glossy. Garnish with chopped parsley if desired.

Serve hot over steamed basmati rice with warm naan for dipping.