Stir together the chilli sauce, soy sauce, vinegar, the minced chile pepper, 2 teaspoons of the sesame oil and 1 tablespoon water in a small bowl. Pour into a small serving bowl and top with the sliced chilli pepper. Set aside to let the flavors blend while making the flatbread.
Heat a medium nonstick pan over medium heat and add the sesame seeds. Cook, stirring, until toasted, about 3 minutes. Pour into a small bowl. Add the spring onions and remaining 1 teaspoon sesame oil to the bowl and set aside.
Roll the dough out on a lightly floured surface until it is about 1/8-inch thick. Sprinkle with the scallion mixture and salt and fold in half like a book. Press the halves together with your fingers and then roll the dough out again until it is 1/8-inch thick. Cut the dough into 6 equal pieces. Stretch and roll each piece until very thin, pinching the edges together to keep the filling from spilling out. You should be able to see the filling through the dough when it is thin enough and the pieces should be 7 to 8 inches in diameter, although they need not be round.
Heat 1/2 tablespoon of the oil over medium-high heat in the same pan the sesame seeds cooked in. When very hot, add a piece of the dough and cook, turning once, until it is puffed and cooked through and has some charred spots, about 2 minutes per side. Transfer to a cutting board and repeat with the remaining pieces of dough, adding more oil as needed to just lightly coat the bottom of the skillet and reducing the heat if the dough starts to burn before it cooks through.
Cut the flatbreads into pieces and serve with the dip and cooked prawns.