Heat a large skillet over medium-high heat. Add ground beef and cook for 6–8 minutes, breaking it apart until fully browned. Drain excess grease if needed. Reduce heat to medium and add minced garlic and grated ginger. Cook for 30 seconds until fragrant. In a small bowl, whisk together soy sauce, brown sugar, sesame oil, rice vinegar, and red pepper flakes. Pour the sauce into the skillet and stir well. Simmer for 3–4 minutes until slightly thickened and glossy. Remove from heat. Divide cooked rice into bowls and spoon the beef mixture over the rice. Garnish with green onions and sesame seeds. Serve warm.