In a large mixing bowl, combine the all-purpose flour, rice flour (if using), and salt.
Add the egg and cold water to the flour mixture. Mix until smooth and well combined.
Gently fold the green onions and seafood mix (if using) into the batter until evenly distributed.
Heat 1-2 tablespoons of vegetable oil in a large non-stick skillet over medium-high heat.
Pour half of the batter into the skillet, spreading it out evenly to form a pancake.
Cook for about 3-4 minutes on each side, or until the pancake is golden brown and crispy.
Remove the cooked pancake from the skillet and drain on paper towels. Repeat with the remaining batter, adding more oil if needed.
In a small bowl, whisk together the soy sauce, rice vinegar, sugar, sesame oil, minced garlic, sesame seeds, chopped green onion, and red chili flakes (if using).
Cut the pajeon into wedges or bite-sized pieces.
Enjoy your meal!