Add green onion, ginger, garlic, soy sauce, red pepper flakes, cornstarch and beaten egg white. Stir well to combine.
Divide the mixture among 4 slices of white sandwich bread and spread it evenly. Sprinkle with sesame seeds and top each slice with another slice of bread, pressing it slightly.
Place a large skillet or cast iron pan over medium-high heat and add about ⅛ inch of oil. Heat until shimmering.
Fry the sandwiches until golden, for about 2-3 minutes, flip and fry for another 1 minute. Transfer to a surface lined with paper towels to drain excess grease. Sprinkle with sesame seeds.
Cut each slice diagonally to create a triangle.
Serve immediately with sesame seeds, green onions and soy sauce on the side.