Prepare the noodles according to the package directions (see note).
Cut flank steak into thin strips, about 2 x 1/4 inch each (5 cm x 1/2 cm).
In a medium bowl, mix 1 tbsp of cornstarch and 1 tbsp of soy sauce.
Toss the beef strips in the soy sauce mixture and marinate for 10 minutes to tenderize (you can skip this step if in a rush).
In a medium bowl, mix 2 tbsp soy sauce, hoisin sauce, sugar and ginger. Reserve.
Place a large skillet or wok over medium-high heat and add vegetable oil.
When the oil is hot, add the beef strips and stir fry for 2-3 minutes until the beef is no longer pink.
Add the minced garlic, sliced carrots and broccoli. Stir fry for 5 minutes or until vegetables are tender.
Add lo mein to the beef/vegetable mixture and toss with the reserved lo mein sauce and sesame oil.
Garnish with optional sesame seeds and serve immediately.