Cook Aromatics: Heat oil in a large pan. Sauté onions until golden. Add garlic and ginger, and cook for 1-2 minutes.
Add Spices: Stir in cumin, coriander, turmeric, chili powder, and garam masala. Cook for 1-2 minutes.
Simmer Sauce: Add crushed tomatoes, tamarind paste, and sugar. Cook for 5-7 minutes until thickened.
Cook Chicken: Add chicken pieces and stir to coat. Cover and simmer for 20-25 minutes, until chicken is tender.
Garnish and Serve: Stir in cilantro and serve with rice or naan.