Heat oil in a large nonstick skillet over medium heat. Add onion, ginger, and garlic; cook 5 minutes. Stir in garam masala, mustard seeds, and red pepper; cook 2 minutes, stirring frequently. Stir in coconut milk and remaining ingredients except cilantro; bring to a boil.
Reduce heat, and simmer 35 minutes, stirring occasionally. Remove from heat; stir in chopped cilantro.