1. Heat a deep pan with oil.
2. Put in the onions, chilies, garlic and ginger. Sauté till the onions are caramelized.
3. Add in the tomatoes and sauté till it becomes tender.
4. Add in the banana and sauté for a minute.
5. Pour in the coconut milk and fish sauce. Bring it to a boil.
6. Put in the prawns, add curry powder and lime juice.
7. Simmer until the prawns are cooked.
8. As the curry is in the make, cook the brown rice in a deep pan or in a rice cooker.
9. Serve the curry over rice in a bowl immediately.