For the dipping sauce: In a small bowl, mix together the soy sauce, vinegar, gochugaru, sesame oil, sesame seeds and spring onions and set aside.
For the batter: In a large bowl, gently whisk together the water, rice flour, self-rising flour, dwenjang, black pepper and salt until smooth. Add the prawns, spring onions, scallops, red chiles, garlic and green chiles and mix to coat well and evenly.
Heat 3 tablespoons vegetable oil in a large nonstick skillet over medium-high heat. Once hot, spoon in one-third of the batter and spread out evenly to make a rectangular pancake measuring about 6 by 7 inches (15 by 18 centimeters). Fry until golden brown and crispy on the bottom, 3 to 4 minutes. Flip over carefully and cook until the other side is golden, another 3 to 4 minutes. Drain on paper towels. Working in batches, make 2 more pancakes, drizzling in more oil as necessary, about 2 to 3 tablespoons per pancake, and adjusting the heat down as needed.
Cut the pancakes into pieces of desired size and transfer to a serving plate. Serve immediately with the dipping sauce.