Make the marinade: Using a mortar and pestle, crush the lemongrass. Add the garlic and chiles, and crush. Add the oyster sauce and stir with a spoon. Rub the marinade onto the meat and marinate for at least 30 minutes or up to overnight.
Make the sauce: Using a mortar and pestle, combine the garlic, chile, and a little bit of sugar, and beat until it forms a paste. Mix in the rest of the sugar, then add the fish sauce and lime juice. Place in another container and keep in the fridge.
Boil the noodles according to the package instructions and wash with cold water to chill them.
Pan-fry the meat or grill it on skewers if you have a grill.
Finely cut all of the vegetables and pick the herbs.
Build the bowl: Place the noodles in the bowl and distribute all the other ingredients on top. Dress with the sauce.
*I prefer the Megachef brand of fish sauce. It has a lot of umami flavor. If you are at the store comparing fish sauces, compare the sodium content and the protein. High protein and low sodium is what you are looking for. More protein means more unmami from the fish and less sodium means the fish sauce relies on more fish for flavor.