01 - Arrange the sliced flank steak strips evenly across the bottom of the slow cooker insert.
02 - Layer the sliced bell peppers, onion, and minced garlic over the beef.
03 - In a mixing bowl, whisk together the soy sauce, beef broth, tomato paste, brown sugar, cornstarch, black pepper, and salt until smooth and well combined.
04 - Pour the sauce mixture evenly over the beef and vegetables in the slow cooker.
05 - Cover and cook on low for 6 hours or on high for 3 hours, until the beef is tender and the vegetables are cooked but still retain a slight crispness.
06 - Stir the contents well. Garnish with sliced green onions and sesame seeds if desired.
07 - Serve hot over steamed rice or noodles.