Heat a wok or frying pan and add 3 tablespoons oil. When the oil is hot, add the garlic and stir-fry briefly until fragrant. Add the sliced beef. Brown briefly, then stir-fry until it is nearly cooked through. Remove from the wok.
Add 1 tablespoon oil in the middle of the wok. Add the broccoli. Stir-fry briefly, then add the mushrooms and the red pepper.
Add beef, beef broth and the cornstarch/water "slurry." Add teriyaki sauce.Turn up the heat and stir to thicken. Sprinkle the sugar over top. Mix everything together and serve hot with rice.