Combine flour and salt in large bowl; whisk to combine. Using wooden spoon, stir in boiling water and 2 teaspoons sesame oil until shaggy dough forms. Turn out dough onto lightly floured surface. Knead until smooth, about 5 minutes, adding flour as needed to prevent sticking. Cover dough with plastic wrap; rest 30 minutes at room temperature.
Divide dough evenly into 8 pieces. Working one at a time, roll dough on lightly floured surface into 3 x 8 x 1/16inch rectangle. Brush dough liberally with sesame oil and top each with 1/4 cup scallions. Roll each rectangle up like a jelly roll, then twist roll into tight spiral, tucking in the end underneath. Cover with plastic wrap and repeat with remaining dough. Rest for 15 minutes at room temperature.
Working on a lightly floured surface, roll 1 dough piece at a time into a 5inch round; set aside. Keep remaining dough pieces covered. Repeat with remaining dough, using parchment to separate pancakes.
Heat 1 teaspoon vegetable oil in medium nonstick skillet on medium heat until hot. Cook each pancake until golden brown and crisp on both sides, about 6 minutes, turning as needed to prevent burning. Remove from pan and immediately drape over thick handle (like a wooden spoon) to form a taco shell. When cooled the scallion pancake will hold its shape.