For the meatballs: Preheat the oven to 425 F. Line a baking sheet with parchment paper.
Combine the beef, panko, egg, soy sauce, gochujang, ginger, garlic, sesame oil and 1/2 teaspoon salt in a medium bowl.
Use a 1-ounce ice cream scoop to form the beef mixture into meatballs (about 20 total) and place on the prepared baking sheet. Roll each meatball by hand to round out the shape. Bake until browned and just cooked through, about 10 minutes.
For the glaze: Whisk the brown sugar, soy sauce, vinegar, gochujang, cornstarch and 1/2 cup water together in a small bowl. Add to a large nonstick skillet and bring to a boil over high heat. Cook until slightly thickened, about 2 minutes.
Add the meatballs and cook, tossing to coat, until evenly glazed, about 1 minute.
Transfer to a serving platter and top with some sesame seeds and scallions.
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