Put beef in a large bowl then add red chili paste, soy sauce, vinegar, sugar, onions, scallions, garlic, ginger and black pepper. Toss until fully coated.
Cover the bowl and let marinade in the fridge for at least an hour to overnight.
When ready to cook, heat up oil in a large pan over medium high heat.
Add the whole mixture into the pan and let it cook until the beef is tender and sauce has thickened a little (about 5 to 7 minutes).
Serve with steamed rice and a side of vegetables, and garnish with scallions or sesame seeds. Enjoy!