In a mixing bowl, combine the soy sauce, red pepper flakes (if using), ginger, garlic, sesame oil, sugar, rice wine (mirin), salt and pepper.
Fold through the pear and sesame seeds. Mix until just combined.
Add the beef pieces, coat well. Cover, place in fridge, and marinate beef for at least 20 minutes (overnight for best flavor).
Heat oil in a frying pan. Once hot, add the chopped onion and carrots, and cook for about 2 to 3 minutes.
Add the beef pieces (including the marinade). Cook for about 3 - 5 minutes or until the beef is cooked through and browned. Stir occasionally. Turn off heat.
Serve with rice, and a sprinkling of extra sesame seeds.