Finely chop the onion and green onion.
Beat the eggs and mix with a pinch of salt.
Heat cooking oil in a pan and stir-fry ground beef.
Add the onion and green onion, and stir-fry together.
Season with soy sauce, sugar, and mirin.
When the beef is cooked, push it to one side of the pan and pour in the egg mixture to scramble.
Serve the cooked beef and scrambled eggs over rice to complete the rice bowl.