Heat oil in a large heavy skillet over medium heat. Add the chicken and cook 2-3 minutes; add onions and cook an additional 3 minutes. Add the crushed ginger, garlic, cumin, garam masala, chili powder, and salt; cook well until fragrant, about 2 minutes. Stir in tomatoes and simmer for 5 minutes. (You can make the dish ahead of time up to this point.) Mix flour with yogurt and add with the milk to the pan. Simmer on low heat until sauce thickens, about 10 minutes. Top with cilantro. Serve with Bamati Rice or steamed broccoli.