Set a large saucepan over medium heat and add 2 tablespoons of gochujang paste, 1 tablespoon light soy sauce, 2 teaspoons fish sauce, and 2 tablespoons of chili oil. Stir for a minute or two, then add the garlic and ginger and cook, stirring, for another minute.
Pour in the coconut milk, lemongrass pieces (if you’re using it), and vegetable broth. Stir to combine everything, then bring it to a simmer, lower the heat, and leave it for five minutes to slightly thicken.
Add your noodles directly into the broth, stir, then let them cook for about 4 minutes. Use your packet to guide you on the cooking time here – different noodles have slightly different cooking times. Once they’re almost ready, add the sliced pak choi and stir through the broth for a minute, until they look bright green. Remove the pot from the heat.
Divide the saucy noodles and pak choi between bowls, spooning lots of the lovely sauce into each bowl. Squeeze a wedge of lime over each bowl, then top with the scallions and cilantro leaves. Finish with another drizzle of chili oil, then serve with more lime wedges on the side.
