1. 1. Heat a pan over medium heat and add the lean ground beef.

2. 2. Cook the beef until browned, then add the diced onion and bell pepper.

3. 3. Stir-fry the mixture until the vegetables are tender and the beef is cooked through.

4. 4. Season with salt, pepper, and your favorite stir-fry sauce.

5. 5. Serve hot and enjoy!