Preheat the oven to 375°F (190°C) and line a baking sheet or loaf pan with parchment paper.
In a small bowl, whisk together the ketchup, 1 tablespoon of gochujang, and the brown sugar to create the glaze.
In a large mixing bowl, combine the ground beef, panko breadcrumbs, eggs, milk, remaining 2 tablespoons of gochujang, soy sauce, sesame oil, ginger, garlic, sliced scallions, and black pepper.
Gently mix the ingredients by hand until just combined, avoiding overworking the meat to maintain texture.
Shape the mixture into a 9x5-inch loaf and place on the prepared baking sheet.
Bake for 40 minutes.
Remove from the oven and brush the prepared gochujang glaze evenly over the top and sides of the meatloaf.
Return to the oven and bake for an additional 15 minutes, or until the internal temperature reaches 160°F (71°C).
Allow the meatloaf to rest for 10 minutes before slicing to ensure moisture retention.