Combine dough ingredients, adding the flour gradually until the dough pulls away from the bowl.
Form a ball, cover with plastic wrap, and let rest 30 minutes at room temperature.
Meanwhile, saute scallions and garlic in oil. Remove from heat and let cool, then add remaining filling ingredients and stir to mix.
Form the dough into 1-inch balls and flatten to be 1/8 inch thick. Place a heaping teaspoon of filling in the center of each. Fold in half to make a half-moon shape and press on edges to seal. Place on a greased or nonstick baking tray.
Brush with the egg mixture and sprinkle sesame seeds on top.