Pour 2 tbsp soy sauce and sugar sliced steak. Marinate at least 30minutes or up to 4hours daily. While the beef is marinating, prep the rest of the ingredients.
In a small-bowl mix the beef broth, cornstarch, the remaining 2tbsp soy sauce. Whisk till combined. Put aside.
Heat 1 tbsp vegetable oil in large-skillet over medium-high. Add half of the beef and cook till browned around the edges.
Turn the beef pieces over and continue cooking for a few minutes. Remove to a plate and keep warm. Repeat with another tbsp of oil and much more sliced beef till all meat is browned.
Pour the last tbsp of oil to the pan. Then add the black pepper, onions and bell pepper. Sauté till the veggies are crisp tender and slightly charred, for 5-8minutes.
Reduce the heat to moderate. Then add ginger, garlic and crushed red pepper flakes, if using. Sauté, stirring continuously till the garlic is fragrant for a few minutes.
Return the cooked beef into the pan, together with any accumulated juices, along with the beef broth mix. Cook till the sauce thickens, for 3-5minutes.
Gently fold in the tomatoes and stir to coat. Remove from the heat and serve immediately. (You can garnish with extra parsley and black pepper and serve over hot cooked rice).