Preheat your oven to 400°F (200°C). Line a large baking sheet with parchment paper.

In a large bowl, gently combine the ground beef, Panko breadcrumbs, egg, green onions, 3 cloves of minced garlic, 1 tbsp grated ginger, 1 tbsp soy sauce, and 1 tsp sesame oil. Do not overmix. Roll the mixture into 1.5-inch meatballs and place them on the prepared baking sheet.

Bake for 15-20 minutes, or until the meatballs are cooked through and lightly browned.

While the meatballs cook, combine the gochujang, 1/3 cup soy sauce, brown sugar, rice vinegar, 1 tbsp sesame oil, 2 cloves minced garlic, and 1 tsp grated ginger in a medium saucepan. Whisk to combine and bring to a simmer over medium heat.

In a small bowl, create a slurry by mixing the cornstarch and cold water. Pour the slurry into the simmering sauce and whisk continuously for 1-2 minutes until the sauce has thickened.

Add the cooked meatballs to the saucepan and gently toss to coat them completely in the sauce. Simmer for 2-3 minutes. Garnish with sesame seeds and sliced green onions before serving.