Against a grain, start slicing your beef into 2-inch long and 1/4 –inch thick slices.
Mix the soy sauce and cornstarch in a bowl. Transfer your beef to the bowl, cover it with plastic wrap and let it marinate for 30 minutes at least and up to 4 hours in the refrigerator.
On medium-high heat, put a skillet containing the oil.
When the skillet is hot enough, add in the garlic and ginger. Mix well till they’re browned enough.
Add in the marinated meat with its sauce. Cook the beef for 2-3 minutes.
Add to the skillet the brown sugar, beef broth, and green onions. Stir fry them for 1-2 minutes. Transfer your beef to a plate.
In the same skillet with the remaining sauces, add another tablespoon of oil. Add in the vegetables of your choice and stir fry them for a couple of minutes.
Bring back the beef to the skillet to mix it with the vegetables. You can also add noodles in this step.
Dish it up while hot with a sprinkle of chopped green onions and enjoy!