Mix flour and salt in the bowl of a stand mixer. Add boiling water and mix briefly with the dough hook attached until large flakes have formed. Add the cold water and knead for another 5 minutes until you have a smooth dough.
Grease a bowl (you can use the same bowl) with 1 tsp oil, place the dough in it, and cover with a wet tea towel or plastic wrap. Let the dough rest for 30 minutes.
Meanwhile, finely chop the scallions and mix all ingredients for the dipping sauce in a small bowl.
Knead the dough for another minute by hand. Then, divide it into 6 equal parts and form each one into a ball.
Grease your working surface with some oil. Starting with one dough ball (cover the rest of them with a damp kitchen towel), roll it out into a thin rectangle using a rolling pin. Sprinkle with ⅙ of the chopped scallions, leaving a ½-inch border at the top and on the sides. Roll it up tightly, then roll it into a snail form.
Roll the filled dough into a thin disc using a rolling pin. → It’s ok if air bubbles burst through and scallions are falling out.
Heat a skillet over medium-high heat with 1 tbsp vegetable oil. Fry each side for 1-2 minutes until golden brown.
Repeat those steps with the remaining dough. Adding more oil to grease your working surface and into the hot skillet for frying if necessary.
Serve hot with the dipping sauce.