Step 1

To prepare sauce: Combine gochujang, lemon juice, ginger, soy sauce, sherry, sesame oil and sugar in a small bowl. Place near the stove.

Step 2

To prepare stir-fry: Heat a 14-inch flat-bottom carbon-steel wok over high heat. (You'll know it's hot enough when a bead of water vaporizes within 1 to 2 seconds of contact.) Add 1 tablespoon oil and swirl to coat. Add steak and stir-fry until just cooked, 2 to 4 minutes. Transfer to a large plate.

Step 3

Swirl in another 1 tablespoon oil; add broccoli and scallions. Stir-fry for 2 minutes.

Step 4

Swirl in the remaining 1 tablespoon oil; add garlic and mushrooms. Stir-fry until the vegetables are tender, 2 to 4 minutes more.

Step 5

Return the steak to the wok. Add the reserved sauce and cook, gently stirring, until well coated and hot, 1 to 2 minutes.