In a mixing bowl put 1 tbsp of ginger garlic paste, 1 tsp of crushed black pepper, 2 tbsp of Soya sauce, 1 tbsp of oyster sauce. 1 tbsp of corn flour, 1 tbsp of vinegar, 1 tbsp of brown sugar and salt to taste. Mix well. Add the 1/2 kg beef slices to the marinade and leave aside. Heat oil in a pan and cook the beef slices from both the sides. When the color starts changing remove the beef slices. In a separate pan. Then in a pan heat 1 tbsp of oil and fry 2 chopped onions in it for 1-2 minutes. In the end spread the fried onions on a sizzling plate and put the fried beef slices on it and serve it.