Prepare the beef by slicing it thinly against the grain.
Marinate the beef with soy sauce, rice vinegar, and garlic.
Coat the marinated beef in cornstarch.
Heat sesame oil in a large pan over medium-high heat.
Fry the beef in batches until golden brown and crispy.
Remove the crispy beef and drain on paper towels.
In the same pan, add bell pepper, ginger, and green onions, sautéing for 2-3 minutes.
Add the crispy beef back into the pan with chili paste and stir well.
Cook for an additional minute to heat through and serve hot.