16 ounces thin flank steak*, chopped into 2-inch pieces
½ white onion, chopped
¼ cup sliced green onions

Sauce:
2 tablespoons + 2 teaspoons sesame oil
1 tablespoon minced garlic
1 red pepper, seeded and thinly sliced
3 tablespoons soy sauce
2 tablespoons brown sugar
1 tablespoon rice vinegar
½ cup water
½ teaspoon crushed red pepper
¼ cup cold water + 1 tablespoon corn starch
sesame seeds for garnish