Heat the vegetable oil in a large skillet or wok over medium-high heat.
Add the sliced flank steak and season with salt and pepper. Stir-fry for about 3-4 minutes until browned. Remove the beef from the skillet and set aside.
In the same skillet, add the minced garlic and ginger. Stir-fry for about 30 seconds until fragrant.
Add the broccoli florets and stir-fry for another 3-4 minutes until they are bright green and tender-crisp.
In a small bowl, whisk together the soy sauce, oyster sauce, cornstarch, beef broth, sesame oil, and sugar.
Pour this sauce over the broccoli in the skillet. Return the beef to the skillet and stir to combine.
Cook for an additional 2-3 minutes until the sauce thickens and everything is heated through.
Serve the beef and broccoli over cooked rice.