Heat oil in a pan over medium-high heat. Splutter mustard seeds. Add onion, and sauté for 2 minutes, stirring occasionally, until it turns light brown. Add green chillies and curry leaves. Saute for few seconds. Add ginger paste and garlic paste. Saute for another minute, stirring occasionally. Reduce heat to low. Add ground turmeric, ground coriander, garam masala, and chilly powder. Saute for few seconds, stirring continuously. Add tomatoes, and sauté until it starts to break down.

Increase the heat to medium-high. Add okras and enough salt. Mix well. Add enough water. Cook, covered, for 4-5 minutes. Stir occasionally. Add coconut milk. Mix well. Simmer for another minute. Remove from flame.