Heat the coconut oil in a large pot over medium heat. Add the chopped onion and sauté until soft and translucent (about 3 minutes). Stir in the garlic and ginger, cooking for 1 minute until fragrant.

Add the red curry paste to the pot. Stir it into the onion mixture for 1-2 minutes to “wake up” the spices.

Pour in the coconut milk and broth, then add the fish sauce and brown sugar. Stir well to combine. Let the broth simmer gently for 5 minutes to blend the flavors.

Add the bell pepper and mushrooms to the pot. Simmer for 3-4 minutes until slightly softened. If using cooked chicken or shrimp, add it now to heat through. For tofu, add it here to soak up the broth’s flavor.

Stir in the lime juice and taste the soup. Add more salt or lime if needed. Remove from heat and top with fresh herbs before serving.