Start by whisking together soy sauce, honey, brown sugar, sesame oil, rice vinegar, garlic, ginger, red pepper flakes, salt, and pepper. Place the thinly sliced flank steak in the mixture and let it sit for 10–15 minutes. This quick marination boosts flavor without toughening the meat.
While the beef marinates, rinse and cut broccoli into florets. Toss the broccoli in a small amount of the marinade to coat lightly. This ensures that the broccoli absorbs the delicious sauce and cooks evenly on the sheet pan.
Preheat the oven to 425°F (220°C). Spread the marinated beef evenly on the sheet pan, followed by the broccoli. Make sure not to overcrowd the pan, so everything roasts rather than steams.
Place the sheet pan in the oven and bake for about 10 minutes. Check that the beef is cooked through and the broccoli is fork-tender but still crisp. The quick bake keeps flavors concentrated and textures perfect.
Once cooked, sprinkle with sesame seeds and sliced green onions. Drizzle with any leftover sauce if desired, and serve immediately while hot. This finishing touch adds visual appeal and extra flavor.