Cook the rice: Start your rice so it's ready when the beef is, about 20 minutes for stovetop white rice.
Brown the beef: Brown the ground beef in a large skillet over medium-high heat, breaking it up as it cooks, about 6-7 minutes. Drain off the excess grease.
Make the sauce: Whisk together the soy sauce, brown sugar, sesame oil, garlic, ginger, and gochujang (if using) in a small bowl.
Simmer: Pour the sauce over the browned beef and simmer 3-4 minutes, stirring, until it thickens slightly and coats the meat.
Serve: Spoon the beef over bowls of rice and top with green onion and sesame seeds.
Notes
Brown the beef well before adding the sauce, that crust is where most of the flavor comes from. Leave out the gochujang for a milder, kid-friendly version.