Cook noodles in a large saucepan of salted boiling water for 1-2 minutes. Drain, return to pan and cover to keep warm.
Heat oil in wok over high heat until just smoking, swirl to coat. Add garlic, ginger, fish sauce and beef mince, cook stirring with a spatula to break up any lumps, for 8 minutes. Remove from wok and set aside.
Return wok to high heat, add brown sugar and 1/3 cup water. Cook for 3 minutes.
Return beef mince to wok, add cashews and cook, stirring constantly to prevent catching for 5 minutes. Add sugar snap peas and broccolini, cook for 5 minutes. Add noodles to pan or place on plate and top with beef mixture. Scatter with herbs and serve.
