Heat a saucepan on a high heat and add 800mls of veg stock.
Add the lemongrass stalks and bring to a boil for about 6 minutes.
Reduce heat to a simmer and add the garlic, chili, chili flakes and lime juice.
Add the sliced pepper, mushrooms, cherry tomatoes and prawns simmering for 5 minutes.
Reduce heat and add the vermicelli noodle blocks.
Stir carefully to separate the noodles.
Add the light coconut milk, coriander and oyster sauce.
Stir well and season with black pepper.