Heat oil in a pan on medium heat and add mustard seeds. Once seeds start to pop, add onions, serrano pepper and curry leaves.Once onions begin to brown, add garlic and gingerAdd the rest of spices and let them bloom - then add ground beef.Stir-fry the beef with the masala mixture in the pan until the beef is mostly browned then add the vegetables and ¼ c water. Cover the pan and cook for 5 minutes.Add coconut milk and continue to simmer until the vegetables are tender (15 minutes).Adjust salt and pepper and add water if you want a thinner curry.Garnish with cilantro and serve.