Begin by thinly slicing the flank steak against the grain. Place the sliced beef in a large Ziploc bag and sprinkle in cornstarch. Seal the bag and shake gently until coated.

Heat a large skillet over medium-high heat and add olive oil. Once shimmering, add the beef in a single layer. Cook for 3-4 minutes on each side until browned and cooked through. Transfer to a plate.

In a mixing bowl, whisk together soy sauce, water, brown sugar, rice vinegar, sesame oil, ginger, garlic, honey, and cornstarch until smooth.

Pour the teriyaki sauce into the skillet over medium heat. Let simmer for 2-3 minutes until thickened.

Return the beef to the skillet and toss to coat in the sauce. Cook for an additional minute. Serve hot, garnished with sesame seeds and green onions.