Step 1: Marinate the Beef : Combine soy sauce, rice vinegar, and cornstarch. Add beef slices and toss to coat. Let it rest for 10β15 minutes to tenderize and absorb flavor.
Step 2: Make the Teriyaki Sauce : In a small saucepan, combine soy sauce, honey, mirin, sesame oil, garlic, and ginger. Bring to a gentle simmer. Stir in the cornstarch-water mixture and cook until glossy and slightly thickened.
Step 3: Cook the Beef : Heat vegetable oil in a large skillet. Add beef and stir-fry for 3β5 minutes until browned and cooked through. Remove from the pan and set aside.
Step 4: Stir-Fry the Vegetables : Add sesame oil to the same skillet. Toss in broccoli, bell pepper, carrots, and zucchini. Stir-fry for about 4β5 minutes until slightly softened but still crisp. Add a splash of soy sauce and sprinkle sesame seeds.
Step 5: Combine and Serve : Return beef to the skillet with the vegetables. Pour in the teriyaki sauce and toss everything to coat evenly. Serve over rice, and garnish with green onions and sesame seeds.