Heat oil in your wok or pan over medium heat.
Add the onion and cook until softened, about 3 minutes.
Add the garlic and ginger, cook for another minute until fragrant.
Increase heat to medium-high and add the beef mince. Cook, breaking it up with your spoon, until browned.
Stir in the soy sauce, brown sugar, and black pepper.
Add the chopped vegetables and cook for an additional 5 minutes, or until slightly softened.
In a separate bowl, soak the vermicelli noodles in hot water for 5 minutes according to package instructions. Drain and cut into shorter pieces with kitchen scissors.
Add the vermicelli and chicken broth to the wok. Bring to a simmer.
In a small bowl, whisk together the cornstarch and water to form a slurry. Gradually add the slurry to the wok while stirring, until the sauce thickens slightly.
Cook for another 2-3 minutes, or until the vermicelli is cooked through and the sauce has reached your desired consistency.