Whisk 2½ cups flour and 1 tsp. salt in a large bowl. Mix in sesame oil and 1 cup boiling water with a wooden spoon until a shaggy dough forms.
Turn out dough onto a lightly floured surface and knead, adding flour as needed to prevent sticking, until dough is smooth, about 5 minutes. Cover with plastic wrap; let rest at room temperature 1 hour.
Divide dough into 8 pieces. Working with one at a time, roll out on a lightly floured work surface as thin as possible (each should be approximately 10" in diameter). Brush about 2 tsp. chicken fat on dough and top with about ¼ cup scallions; season with salt. Roll dough away from you (like a jelly roll) into a thin cylinder, then, starting at 1 end, wind roll onto itself to create a coil (like a cinnamon roll). Cover with plastic wrap and repeat with remaining dough. Let rest at room temperature 15 minutes.
Working with 1 coil at a time, roll out on a lightly floured surface to a 5" round (keep other coils covered). Repeat with remaining dough and stack as you go, separating with parchment or lightly greased foil brushed with vegetable oil.
Heat 1 Tbsp. vegetable oil in a medium skillet over medium-low. Working with one at a time, cook pancake, turning frequently to prevent scallions from burning, until golden brown and crisp on both sides and cooked through, 8–10 minutes. Transfer pancakes to a wire rack and let rest about 5 minutes before cutting into wedges.
Whisk vinegar, soy sauce, chili oil, sugar, and red pepper flakes in a small bowl until sugar is dissolved. Serve alongside pancakes for dipping.