Combine the flour and salt in a mixing bowl. Add the eggs and water, mixing well with your hands. Add more water if needed to form a soft dough. Cover and set aside for at least 30 minutes.
Grate or mince the onions and place them in a colander or sieve set over a bowl; drain the juice and discard. Combine the onion, beef mince, salt and pepper; mix the meat well with a spoon until mashed.
Divide the dough into two portions and lightly flour a work surface. Keep one piece of dough covered while you roll out the second portion into a rectangle, rolling the dough as thin as you can. Cut the rectangle into 5cm squares with a knife or pastry wheel.
Place about 2 teaspoons of the meat filling in the center of each square. Seal the dumplings by gathering the edges of the dough and pinching them together at the top to form a bundle. Transfer the finished dumplings to a floured plate and sprinkle more flour over to prevent sticking. Repeat with the second piece of dough.
Heat the oil and chilli flakes in a small frypan over low heat just until the pepper flakes have started to colour the oil; don't let them burn. Remove from the heat and keep warm. Stir the minced garlic into the yoghurt and set aside.
Bring a large pot of salted water to a boil over medium-high heat and cook the dumplings until the filling is no longer pink and the dough is tender, 20 to 25 minutes. Drain well. Divide the dumplings among four plates. Spoon the yoghurt sauce over and drizzle each serving with the hot pepper oil.