Prepare the teriyaki marinade first. Combine in a large bowl the soy sauce, water, oil, sugar, vinegar and spices. Whisk and set aside.

Use a sharp knife to prepare the steak: trim any silverskin and fatty parts. Slice the steak into long, 1-inch wide strips. Place the sliced steak into the prepared marinade, cover and refrigerate for at least an hour. For best results, refrigerate for 4 to 6 hours, or overnight. Turn the beef every couple of hours.

While the beef is marinating, pre-soak the bamboo skewers in water to prevent the wood from burning. Preheat an outdoor grill to 475F; or stove-top grill to medium-high. Skewer each strip of beef, one to two pieces per skewer. Grill the beef for 4 to 5 minutes per side.

While beef is grilling, finish preparing the teriyaki sauce. Pour the marinade into a small saucepan and bring up to a simmer over medium heat; simmer for 5 minutes. In a small bowl, combine the cornstarch and water, then add the slurry to the sauce. Whisk and cook the sauce for 1 minute, until the sauce is thickened. Use a pastry brush to add more sauce to the beef skewers.

Garnish the beef with sesame seeds and chopped green onions when serving; serve immediately.