Cut the beef into bite-sized pieces.
Slice the onion and chop the green onion.
Heat cooking oil in a pan and stir-fry the beef.
Once the beef is cooked, add the onion and green onion and stir-fry together.
Season with soy sauce, sugar, and mirin.
Place the cooked beef and vegetables on top of rice.
Drizzle mayonnaise to your liking.
Finish by topping with seaweed flakes and sesame seeds.