In a pan, add some vegetable oil and heat it on medium flame. Add 2 tbsp Thai red curry paste to the mixture and simmer it for 30 seconds. To this mixture, add coconut milk, brown sugar, and lemongrass. Give it a good stir and let it sit for 5 minutes.
Once the curry looks ready, add green beans, prawns, and bell peppers/capsicum. Let this mixture cook for a full 5–6 minutes.
Once all prawns are cooked, turn off the flame. Add 1–2 tbsp of Thai fish sauce, basil leaves, and 1 tbsp of fresh lime juice. Let the curry sit for 5 minutes.
Serve hot with steamed rice. For more of a desi twist, eat it will rotis.