Pour 300g warm water into 500g medium gluten flour while stirring gently. Seal the bowl with plastic wrap and let it sit for 40 minutes.
Pre-heat the pan. Pour 100g peanut oil and 100g medium gluten flour. Stir until the paste slightly turns golden. Set it aside and let cool down.
It's time to prepare the meat! Add 3g salt, 2 teaspoons of soy sauce, 250g chopped green onion, 30g chopped ginger, and 50g sesame oil. Stir and set it aside for 15 minutes.
Cut the dough in half, and use a rolling pin to push each half into a sheet of pastry with width < 15mm and thickness < 5mm. Mix 2 tablespoons of vinegar and water together, and apply the mixture on the pastry. Then evenly spread the meat onto the surface. Cut the pastry in half again.
Roll the pastry, and fry it in 150°C peanut oil.
After the surface appear golden, take out the fried meat roll and cut it in slices.