In a large skillet, heat 1 tablespoon of vegetable oil over medium-high heat. Add the ground beef and cook until browned (about 5–7 minutes). Drain excess grease.
Stir in the chopped onion and sauté until softened (3–5 minutes).
Add garlic and red pepper flakes; cook until fragrant (about 1 minute).
Incorporate the broccoli florets and sliced bell pepper, cooking for an additional 2–3 minutes.
In a small bowl, whisk together beef broth, soy sauce, cornstarch, brown sugar, sesame oil, and ginger until smooth.
Pour the sauce over the beef mixture and stir well; bring to a simmer and cook for another 2–3 minutes until thickened.
Season with salt and pepper to taste before serving hot over cooked rice.