2 Tbsp. black (Chinkiang) vinegar or unseasoned rice vinegar
¼ cup plus 2 Tbsp. soy sauce
2½ tsp. sugar, divided
1½ tsp. gochugaru or other mild red pepper flakes, divided
1 16-oz. jar Napa cabbage kimchi
1 lb. ground pork (not lean)
4 scallions, thinly sliced
2 garlic cloves, grated
1 2" piece ginger, peeled, finely grated
¼ cup low-sodium chicken broth or water
3 Tbsp. toasted sesame oil
2 tsp. oyster sauce
1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt
½ tsp. freshly ground white or black pepper
50 fresh or frozen thawed gyoza or other round dumpling wrappers
2 Tbsp. vegetable oil, divided