In a mixing bowl, combine the flour and salt. Gradually pour in the boiling water while stirring with a fork or chopsticks until a shaggy dough forms. Allow it to cool slightly, then knead the dough on a floured surface for about 5 minutes until smooth. Cover with a damp cloth and let it rest for 30 minutes.

After resting, divide the dough into four equal pieces. Roll out one piece into a thin rectangle, about 1/8 inch thick. Brush a thin layer of vegetable oil over the surface, then sprinkle with a quarter of the chopped scallions.

Starting from one edge, roll the dough tightly into a log. Coil the log into a spiral shape and tuck the end underneath. Flatten the spiral gently with your palm, then roll it out again into a circle about 1/4 inch thick.

Heat a skillet over medium-high heat and add 2 tablespoons of vegetable oil. Once hot, place the pancake in the skillet and cook for 2-3 minutes on each side until golden brown and crispy. Repeat with the remaining dough pieces.

For the dipping sauce, mix equal parts soy sauce and rice vinegar in a small bowl. Add sesame oil and chili oil if desired for extra flavor.

Serve the scallion pancakes hot with the dipping sauce on the side.