In a small mixing bowl, whisk together 2 tablespoons of cornstarch, 2 tablespoons of water, and the garlic powder.

Sprinkle the sliced beef with freshly ground pepper. Add the sliced beef to the cornstarch mixture and toss to coat thoroughly.

Heat 1 tablespoon of oil in a large skillet over medium-high heat. When hot, add the beef and cook for about 5 minutes, stirring occasionally, until cooked through.

Transfer the meat to a separate dish and add the remaining tablespoon of oil to the pan. When hot, add the onions, ginger, garlic, and broccoli (and carrots, if using). Stir-fry until the broccoli is tender-crisp, about 4-5 minutes. Return the beef to the pan and cook until heated through.

While the beef is re-heating, whisk together the remaining 1/2 cup water, 1 tablespoon cornstarch, soy sauce, brown sugar, Sriracha, and ground ginger. Add the sauce to the beef mixture and cook for about 1 minute or until the sauce is thickened. Serve immediately over hot rice.