Slice the flank steak thinly against the grain, shred the cabbage, julienne the carrots, and slice the pepper. Have garlic and ginger ready.

Heat a large skillet or wok over medium-high heat. Add the vegetable oil and let it get hot but not smoking.

Season the sliced beef lightly with salt and pepper. Add it to the skillet in a single layer and stir-fry for 3–4 minutes until browned and just cooked through. Remove the beef to a plate and set aside.

In the same skillet, add the minced garlic and ginger. Sauté for about 30 seconds until aromatic—don’t let them burn.

Add the shredded cabbage, carrots, and bell pepper. Stir-fry for 5–6 minutes, tossing often, until the vegetables are tender but still have some crispness.

Return the beef to the skillet. Pour in the soy sauce and sesame oil. Toss everything together so the sauce coats the beef and vegetables. Cook for 2–3 more minutes to heat through and meld flavors.

Sprinkle the sesame seeds over the stir-fry and toss. Taste and adjust salt or pepper as needed.

Serve hot, garnished with sliced green onions.