Heat a large skillet over medium heat and add the ground beef. Cook until browned, draining excess grease if necessary.

Stir in the minced garlic and cook for another minute until fragrant.

Pour in the soy sauce, add the brown sugar, drizzle in the sesame oil, and toss in red pepper flakes if desired. Cook together for a few minutes until the mixture thickens slightly.

Serve the beef over warm, cooked rice, and garnish with sliced green onions.