To make the dipping sauce, combine the vinegar, water and sugar in a medium saucepan over low heat. Cook, stirring, for 2 minutes or until the sugar dissolves. Increase heat to high and bring to the boil. Cook for 5 minutes or until the syrup thickens. Set aside for 10 minutes to cool. Transfer to a bowl. Add the cucumber and chilli and combine. Cover and place in the fridge for 1 hour to chill.
Meanwhile, heat the peanut oil in a frying pan over medium heat. Add the onion, garlic and ginger and cook, stirring, for 5 minutes or until the onion is soft. Add the mince and cook, stirring with a wooden spoon to break up any lumps, for 5 minutes or until mince changes colour. Add the potato and cook, stirring occasionally, for 5 minutes or until just soft. Add the peas and curry powder and cook, stirring, for 2 minutes. Set aside for 30 minutes to cool.
Add the coriander to the beef mixture and stir to combine. Season with salt and pepper. Use a 6cm-diameter round pastry cutter to cut 9 discs from each pastry sheet. Place 2 teaspoons of the beef mixture in the centre of each disc. Brush edges with water and fold in half to enclose filling. Pinch edges together to seal.
Add enough vegetable oil to a wok to reach a depth of 10cm. Heat to 190°C over high heat (when oil is ready a cube of bread will turn golden in 10 seconds). Add 6 curry puffs and deep-fry for 3 minutes or until puffed and golden. Use a slotted spoon to transfer to a plate lined with paper towel. Repeat, in 5 more batches, with the remaining curry puffs, reheating oil between batches.
Arrange the curry puffs on a serving platter and serve with dipping sauce.