Add the beef strips and corn starch to the bowl toss to coat them well.
Heat the olive oil in a large skillet over medium heat.
Add the beef strips and cook until done through, about 5-7 minutes, or until no longer pink.. Remove the beef strips to a plate.
In the same skillet, add the garlic and ginger and cook for about 1 minute, stirring constantly.
Add the broccoli and beef stock, cover, and cook until the broccoli is tender, about 5-7 minutes.
Meanwhile, combine the soy sauce, sherry, and brown sugar substitute in a bowl and whisk well.
Add to the skillet with broccoli along with the beef strips. Cook another 3-5 minutes until the sauce thickens.
Heat the zoodles over medium heat in a separate skillet with a little drizzle of olive oil just long enough to warm them.
Place the zoodles on a dish or in a bowl, and top with the beef and broccoli mixture and sliced green onions, if desired.