In a small mixing bowl, whisk together cornstarch and water until smooth. Then, add in soy sauce, light brown sugar, grated ginger, minced garlic, and red pepper flakes. Set aside.

Wash and cut the broccoli into bite-sized florets. Slice the flank steak thinly against the grain, about ¼ inch thick.

In a large skillet, heat olive oil over medium heat. Add broccoli florets and water, cover, and steam for about 5 minutes. Remove and set aside.

Increase the skillet temperature to high and add another tablespoon of olive oil. Add sliced flank steak in a single layer, searing for 4-5 minutes until browned.

Lower the heat to medium, pour the teriyaki sauce over the beef, stirring continuously for about 2 minutes. Fold in the cooked broccoli.

Remove from heat and garnish with sesame seeds. Serve over steamed rice or noodles.