Start your rice cooking first so it is ready when the beef and broccoli are done. Cook according to the package directions and keep it covered and warm.

Slice the beef as thin as you can manage, cutting against the grain. Against the grain means perpendicular to the long lines of muscle fiber running through the meat. Thinner slices, about 1/8 inch, cook in 60 to 90 seconds and stay tender. Thicker slices take longer and can get chewy. If the beef is slightly frozen, about 20 minutes in the freezer, it is much easier to slice thin.

In a small bowl, whisk together the soy sauce, oyster sauce, brown sugar, garlic, ginger, cornstarch, and water until the cornstarch is fully dissolved and no lumps remain. Set the sauce aside.

Heat 1 tablespoon of the vegetable oil in a large skillet or wok over high heat until it just begins to smoke. Add the broccoli in a single layer and cook without stirring for 2 minutes so it gets a little char on the edges. Stir and cook 1 to 2 more minutes until the broccoli is bright green and just tender but still has some crunch. Transfer to a plate and set aside.

Add the remaining 1 tablespoon of oil to the same skillet over high heat. Add the sliced beef in a single layer, working in two batches if needed to avoid crowding the pan. Crowding causes the beef to steam rather than sear. Cook without moving for 60 seconds, then stir and cook 30 to 60 seconds more until just cooked through. The beef will lose its pink color quickly at this heat.

Return the broccoli to the skillet with the beef and pour the sauce over everything. Toss and stir for about 1 minute as the sauce thickens and coats the beef and broccoli. Once the sauce has gone from thin and watery to glossy and clingy, it is ready. Drizzle with sesame oil if using.

Divide the rice among four bowls. Spoon the beef and broccoli over the rice and top with sliced green onions. Serve immediately.