In a small bowl, combine brown sugar, soy sauce, sesame oil, red pepper flakes and ginger; whisk until well combined.
Heat oil in a skillet over medium high heat. Add garlic; stir and cook for a minute or until fragrant. Add ground beef and cook until browned, about 3-5 minutes, making sure to crumble the beef as it cooks; drain excess fat. Add soy sauce mixture and green onions; stir to combine. Continue to simmer until heated through, about 2 minutes.