Step 1

Place the beef in a bowl and top with 1 tablespoon soy sauce and black pepper. Stir to coat then set aside to marinade while you prepare the rest of the ingredients.

Step 2

Prepare the sauce: In a medium mixing bowl or large measuring cup, stir together the soy sauce, water, maple syrup, rice vinegar, garlic, ginger, red pepper flakes, and cornstarch. Set aside.

Step 3

Continue with the stir fry: In a large, deep sauté pan or wok, heat 1/2 tablespoon oil over medium-high heat. Once the oil is hot but not smoking, add the beef. Cook until the beef is browned on all sides and fully cooked through, about 4 minutes. Remove the beef and any juices that have collected in the skillet to a plate and set aside.

Step 4

Heat the remaining 1/2 tablespoon oil. Add the bell pepper and other vegetables. Cook for 4 minutes, or until slightly softened and lightly browned.

Step 5

When the vegetables are ready, add the water chestnuts and return the beef and juices to the pan. Pour in the sauce and toss to coat. Let simmer 3 to 4 minutes to thicken and warm the beef through. Stir in about half of the green onions. Sprinkle the sesame seeds and remaining green onions over the top. Serve warm, with additional red pepper flakes and/or soy sauce as desired.