In a mixing bowl, blend together plain yogurt, lemon juice, ginger-garlic paste, and salt. Coat the chicken thighs thoroughly in the marinade. Cover and refrigerate for 30 minutes to 4 hours.

In a large skillet, heat olive oil or ghee until shimmering. Add onions and sauté for 5-7 minutes until golden. Stir in garlic and ginger, cooking for 1-2 minutes.

Add pumpkin puree and diced tomatoes to the skillet, mixing well. Cook for 5 minutes, stirring occasionally until heated through.

Reduce heat and stir in heavy cream, chicken broth, and butter. Add brown sugar if desired and let simmer for 15-20 minutes until thickened.

In a separate skillet, cook marinated chicken for 6-8 minutes per side until browned and internal temperature reaches 165°F (74°C).

Transfer the chicken into the pumpkin sauce and stir to combine. Simmer for an additional 5-10 minutes on low heat.

Serve hot over basmati rice or alongside naan bread. Garnish with cilantro if desired.