01 - In a large mixing bowl, combine the ground beef, napa cabbage, onion, green onions, garlic, ginger, soy sauce, sesame oil, mirin, sugar, black pepper, and egg. Mix thoroughly until all ingredients are evenly incorporated.
02 - Place a dumpling wrapper in your palm and spoon 1 rounded teaspoon of filling into the center. Moisten the edge with water, fold into a half-moon shape, and pinch the edges firmly to seal, pleating as desired. Repeat with remaining wrappers and filling.
03 - In a small saucepan, combine the gochujang, honey, soy sauce, rice vinegar, sesame oil, and minced garlic. Simmer over low heat for 2 to 3 minutes until slightly thickened. Remove from heat and set aside.
04 - Heat 1 tablespoon of vegetable oil in a large nonstick skillet over medium-high heat. Arrange the mandu in a single layer and cook for 2 to 3 minutes until the bottoms are golden brown.
05 - Pour ¼ cup of water into the skillet and immediately cover with a lid. Steam for 3 to 4 minutes, then uncover and continue cooking until the water evaporates and the bottoms regain their crispness, about 1 to 2 minutes more.
06 - Transfer the mandu to a serving plate. Drizzle or brush generously with the warm gochujang glaze, sprinkle with toasted sesame seeds, and serve immediately.