Mix ingredients. Combine 1 egg, 2 Tbsp gochujang, and 1 Tbsp soy sauce in the bottom of a large mixing bowl, which helps ensure you never over mix or over work the ground meat. Add ground chicken, ¾ cup breadcrumbs, sliced scallions, and 1 tsp Kosher salt and blend until just combined. (You can also add the wet ingredients on top of the dry; just make sure to mix wet ingredients separately!) Preheat a broiler to high.
Form the meatballs. Use a cookie scoop to portion the meat mixture into meatballs of the same size, roughly 2-inch round. Gently roll into balls, then place on a parchment-lined baking sheet.
Make the sauce. Combine ¼ cup soy sauce, 2 Tbsp gochujang, 2 Tbsp brown sugar, 1 tsp rice vinegar, and 1 tsp sesame oil in a medium bowl, then whisk to combine.
Broil the meatballs. Cook the meatballs on high for 6 minutes, flip once, then cook 6 minutes more.
Toss in gochujang sauce. Immediately toss the Korean meatballs in the sauce, coating evenly on all sides.
Serve immediately. I like to serve these in rice bowls with kimchi or pickled carrots and daikon. Garnish with sesame seeds and thinly sliced green onion, then serve immediately!