Preheat oven to 450°F and line a large sheet pan with parchment paper.
In a large bowl, whisk together soy sauce, sesame oil, honey, garlic, ginger, and red pepper flakes.
Add sliced beef, broccoli, bell peppers, and onion to the bowl and toss until everything is well coated.
Spread the beef and vegetables in a single layer on the prepared sheet pan, making sure not to overcrowd.
Roast for 20-25 minutes, stirring halfway through, until beef is cooked through and vegetables are tender and slightly charred.
Serve immediately over rice or noodles, drizzled with any pan juices.