In a large pot, heat the oil and cook the ginger, lemongrass, and red curry paste for a minute until fragrant.
Pour in the chicken broth, fish sauce, and brown sugar. Simmer for 15 minutes.
Add the coconut milk and mushrooms, and cook for 5 more minutes or until the mushrooms are soft.
Lastly, add the shrimp and cook them just until they lose their transparency, about 3-5 minutes. Check the seasoning and add salt if needed.
To serve, add chopped cilantro on top and extra lime juice if needed.