Add flour and salt to a bowl of a stand mixer. Using a dough hook attachment, mix them together on low. With the mixer still on, slowly drizzle in hot water. Continue mixing until dough forms. If the dough is still sticking to the bowl, add another 2 tablespoons of flour.
Once the dough is smooth, remove from the bowl and knead a few times on a clean counter. Smooth into a ball and cover with plastic wrap. Leave to rest for 30 minutes.
In the meantime, chop the bunch of scallions and discard the bottom roots. Place canola oil in a small sauce pan, along with scallion whites. Set over medium heat. Cook the scallion whites for 5 minutes and then turn off heat. If the scallions are getting too browned, turn off heat sooner. Let scallions steep in the hot oil.
Separate the dough into 5 even sections ( weigh my dough to get this exactly right). Working with one section at a time, roll into a 7-inch, thin pancake. Strain the oil to remove the scallion pieces and keep the oil. Lightly brush with a ultra-thin layer of the scallion oil. Roll up the pancake into a log. Starting at one end, tuck into the center and roll into a snail-like shape. Flatten the roll with the palm of your hand, aiming the seal all the edges into a cohesive disk. Finish rolling with a rolling pin, making it into a 7-inch disk again. Brush with another thin layer of oil. Top with about 3 tablespoons of chopped scallions. Roll again in the same way. Finish by rolling into a 7-inch disk again. Repeat with the other 5 sections of dough.
Place cast-iron skillet over medium heat. Brush a couple tablespoons of oil on the bottom. Once hot, add a pancake and cook until it starts to turn deep golden brown, about 4-5 minutes. Flip and cook for about 4 minutes. Remove from heat. Repeat with the other 4 pancakes.
Serve immediately or refrigerate and reheat within the next 5 days.