In a small bowl, whisk together ¼ cup brown sugar, ¼ cup soy sauce, 2 tsp sesame oil, ½ tsp red pepper flakes and ¼ tsp ginger.
Heat 1 Tbsp vegetable oil in a large cast iron skillet over medium high heat. Add 3 garlic cloves and cook, stirring constantly, until fragrant, about 1 minute. Add ground beef and cook until browned, about 3-5 minutes, making sure to crumble the beef as it cooks; drain excess fat.
Stir in soy sauce mixture and green onions until well combined, allowing to simmer until heated through, about 2 minutes.
Serve immediately. Garnish with green onion and sesame seeds, if desired.
