Slice the beef into thin 2 inch slices. Try to slice the beef after placing it in the freezer for about 1 hour.
Place the sliced beef into a bowl then add 1/2 cup soy sauce, 2 minced garlic cloves, 1 tbsp brown sugar, and 1/2 tsp fresh ginger over the beef. This will be the marinade. Give it a quick stir to ensure that the beef is fully submerged in the marinade. Cover and let it sit for at least 2 hours in the refrigerator.
In a separate bowl combine 1/3 cup soy sauce, 1 cup beef broth, and 2 tbsp brown sugar, 2 pressed garlic cloves, and 1/2 tsp grated ginger.
Dissolve 2 tbsp beef broth with 2 tbsp cornstarch and whisk it into the rest of the sauce ingredients.
Heat about 2 Tbsp avocado or canola oil in a large 14-inch wok to high heat and cook the marinated beef in two separate batches. Cooking in separate batches will help prevent the meat from overcrowding and improperly cooking. Add a tablespoon of oil in between each batch.
Once the beef is fully cooked, remove from the wok and set aside.
In the same wok, stir fry the chopped onion and garlic for about 1-2 minutes on medium-high heat.
Then stir fry the chopped bell peppers. Don't overcook the vegetables. You want them to stay slightly crisp.
Add the beef back into the wok and pour the sauce over. Cook over medium-high heat for 3-5 minutes or until the sauce thickens. Serve over hot rice.