In a bowl, combine 2 tablespoons cornstarch, 2 tablespoons water and garlic powder until smooth.

Add beef and toss.

In a large skillet or wok over medium-high heat, stir-fry beef in 1 tablespoon oil until beef reaches desired doneness; remove and keep warm.

Stir-fry onion in remaining oil for 4-5 minutes until softened. Add the broccoli and cook for 3 minutes until the broccoli is tender but still crisp. Return beef to pan.

Combine soy sauce, brown sugar, ginger and remaining 1 tablespoon cornstarch and 1/2 cup water until smooth; add to the pan.

Cook and stir for 2 minutes.

Serve over rice and garnish with toasted sesame seeds (optional).