In a bowl, combine pork, five spice, first measure of brown sugar, salt and pepper. Toss to coat the pork well, then set aside to marinate for 10 minutes.
Heat oil in a heavy-bottomed medium-size saucepan on medium to high heat. Fry lemongrass for 30 seconds until fragrant then add pork and garlic and continue cooking for 2-3 minutes until pork is browned, being careful not to burn the garlic.
Add soy sauce, water and brown sugar. Bring to a simmer, cover with a tight-fitting lid and reduce to low heat to cook for 1 hour 15 minutes, or until pork is tender. If at any time it looks like the pork is drying out, just add a bit more water, soy sauce and sugar.
When pork is cooked, prepare the noodles. Place noodles in a dish or pot and pour over boiling water to cover. Leave noodles to stand for 5 minutes until soft. Drain and toss noodles with raw beansprouts (this helps cook the beansprouts ever so slightly).
To serve, divide noodles and beansprouts between bowls. Top with chunks of pork (which you can shred roughly if you like) and spoon over some sauce. Finish with cucumber, spring onion, plenty of Asian herbs, peanuts and chilli (if using). Serve with a wedge of lime to squeeze over just before eating.