In a mixing bowl, combine the flour, rice flour (if using), cold water, salt, pepper, and egg (if using). Stir until smooth and well combined.
Mix the chopped green onions, mushrooms, carrots, bell peppers, and seafood (if using) into the batter. Stir to coat the vegetables and seafood evenly.
Heat a non-stick skillet or frying pan over medium-high heat and add a small amount of vegetable oil.
Pour a ladleful of the batter mixture into the skillet, spreading it out into a thin, even layer. You can make one large pancake or several smaller ones, depending on your preference.
Cook for about 3-4 minutes on each side or until golden brown and crispy. Flip carefully to avoid breaking the pancake.
In a small bowl, mix together the soy sauce, rice vinegar, sugar, sesame oil, sesame seeds, minced garlic, and chopped green onions.
Transfer the cooked pajeon to a cutting board and cut into wedges.
Enjoy your meal!