In a large soup pot add chicken stock, lime juice, lemongrass stalks, lime zest and grated ginger.
Bring to a boil, reduce heat to low and simmer for 20 minutes until fragrant.
Remove lemongrass stalks and add in chicken and mushrooms. Increase heat to medium and cook for about 25 minutes until the chicken is fully cooked and the mushrooms are tender.
Add in coconut milk, fish sauce and brown sugar. Stir to combine and simmer for 5 minutes.
Serve in a large bowl topped with desired amount of cilantro, lime wedges and sriracha.
