Prep everything first (mise en place). Slice the flank steak thinly across the grain — cutting across the muscle fibers shortens them and makes the cooked beef tender. Put the sliced steak in a bowl and set the vegetables, garlic, ginger and rice nearby. Stir-fries are fast; having everything ready prevents overcooking.

Make the quick marinade: in the bowl with the beef add 1 tablespoon low-sodium soy sauce, half the grated ginger (1/2 inch worth), half the minced garlic, and a pinch of black pepper. Toss to coat and let sit 5–10 minutes while you heat the pan—this seasons and slightly tenderizes the beef without making it wet (too much liquid will steam instead of sear).

Heat your wok or a large heavy skillet over high heat until very hot — you should see just a faint wispy smoke. High heat is essential to rapidly sear the thin steak slices and vegetables so they brown quickly without becoming soggy.

Add 1 teaspoon neutral oil and swirl to coat the pan. Immediately add half the beef in a single layer (don’t overcrowd — overcrowding drops the pan temperature and causes steaming). Sear without moving for about 45–60 seconds to develop caramelized edges, then toss and sear another 30–45 seconds until just browned but still medium-rare to medium (thin slices cook very quickly). Remove seared beef to a plate and repeat with the remaining beef. Resting the seared slices prevents them from overcooking in the final step.

Lower heat to medium-high, wipe the pan if there are heavy browned bits (but keep the fond — those browned bits add flavor). Add the sesame oil; it’s used here for flavor and a little to coat the vegetables. Add the remaining ginger and garlic and stir for 15–20 seconds to bloom their aromatics — this gentle cooking releases aromatic oils but avoids burning which would become bitter.

Add the broccoli and carrot first and stir-fry 2 minutes. These denser vegetables need slightly more time to become crisp-tender. Toss constantly so they cook evenly and retain bright color and crunch.

Add the red bell pepper and continue to stir-fry 1–1.5 minutes until the pepper is tender-crisp. By adding peppers later you preserve their sweet flavor and vivid color — overcooked peppers become dull and soft.

Return the beef to the pan along with the remaining 1 tablespoon soy sauce. Toss everything together and cook for an additional 30–60 seconds just to reheat the beef and let the sauce cling to the vegetables. This quick finish keeps the beef tender and allows the sauce to glaze the ingredients without pooling.

Taste and adjust: add a tiny pinch of salt if needed and more pepper to taste. If you’d like a glossy, slightly thicker sauce, mix 1 teaspoon cornstarch with 1 tablespoon cold water and stir it in now; cook 30 seconds until glossy (optional).

Serve immediately over warmed brown rice. Garnish with sliced scallions and toasted sesame seeds if using. Serving right away preserves the contrast between the hot beef and vegetables and the nutty rice.