01 - Combine flank steak with soy sauce, cornstarch, and sesame oil. Toss to coat evenly and let rest for 10 minutes.
02 - Whisk together all sauce ingredients in a small bowl; set aside.
03 - Heat 1 tablespoon vegetable oil in a large wok or skillet over high heat. Arrange beef in a single layer; sear 1 to 2 minutes per side until browned. Remove beef and keep warm.
04 - Add remaining oil to the wok. Stir-fry garlic, ginger, and white parts of spring onions for 30 seconds until fragrant.
05 - Add julienned carrots; stir-fry for 2 minutes. Add snow peas and cook for 1 to 2 minutes until tender-crisp.
06 - Return beef to the wok. Pour in sauce. Toss and stir-fry for 1 to 2 minutes until sauce thickens and beef is cooked through.
07 - Sprinkle green parts of spring onions over the top. Serve immediately, optionally with steamed rice.