Place the flour and salt in a food processor and pulse briefly to mix. With the blade running, slowly add the water through the feed tube until a ball forms. Turn out onto a lightly floured surface and knead briefly. The dough should be soft and elastic. Cover with plastic wrap and set aside to rest for 30 minutes to 2 hours, whatever is most convenient.
Mix together cheese and scallions in medium bowl. Set aside.
Cut the dough in half. Set one half aside, covered. On a lightly floured surface, shape the other half into a cylinder by rolling it under your palms. Cut the cylinder crosswise in half, then in half and half again, to give you 8 equal pieces. Work with one piece at a time, leaving the others loosely covered with plastic wrap.
On the lightly floured surface, roll one piece out to a nearly 5-inch round. Place 1 packed tablespoon of the cheese mixture in the center of the round and fold over to make a half-moon shape. Press down lightly with a floured palm, to get rid of air bubbles, then pleat the edges closed.
Start at one end and pinch the edges together between thumb and forefinger, then twist the place over, rolling the edge. Move along about ¼ inch and repeat, then continue until the edge is completely sealed. If the dough is not sticking to itself, brush off excess flour and brush the edge with a very little water. Set aside on a lightly floured surface and repeat with the remaining 7 pieces of dough, and then with the remaining dough and cheese.
Place a large wok or deep heavy pot on stovetop, making sure it's stable. (Or use a deep-fryer.) Pour 2 inches of oil into the wok or pot and heat over high heat. To check temperature of the oil, hold a wooden chopstick vertically in the oil, with the end touching the bottom of the pot. If bubbles bubble up along the chopstick, the oil is the right temperature. The oil should not be smoking.
When the oil is ready, slide one momo into the hot oil. Add another, and repeat until you have 4 frying at once. If pot is small, stop before pot is crowded. Use a slotted spoon or wire skimmer to move the momos around and gently turn them. They will quickly turn golden brown with darker brown bubbled spots.
After 1-2 minutes, when they are a rich golden brown and crisped looking, use the slotted spoon or skimmer to transfer to a rack or plate lined with paper towels. Repeat with the remaining momos.