Heat oil in a wok or large frypan over medium heat. Add lemongrass and garlic, and stir-fry for 30 seconds until fragrant.
Increase heat to medium-high, add pork and cook for 3-5 minutes until no longer pink. Drain excess liquid if necessary.
Add sugar and 1 tablespoon fish sauce, stirring to coat. Add stock and simmer for 5-8 minutes until liquid has evaporated.
Remove from heat, then add sambal and lime juice, tossing to combine.
Meanwhile, cook noodles according to packet instructions, then drain and toss with remaining fish sauce.
Serve pork on noodles with herbs and cucumber.
