Slice steak diagonaly across the grain, into 1/4 inch thick strips. Heat 1 tsp oil in large skillet until oil is hot and seems to be rippling. Add half of meat and stir while cooking for 30-40 seconds until meat is no longer pink. Remove meat from pan to a serving bowl. Add another 1 tsp oil to skillet and cook the second half of the meat the same way. Remove it from pan to the bowl also. Add 2 T teriyaki sauce to meat and stir.
Return skillet to heat and place 2 tsp oil in it. When ready to stir fry add bok choy. Stir fry about 30 seconds, then add 3 T water, cover skillet and steam for about 1 minute. Uncover, add remaining teriyaki sauce and stir fry for about 1 minute until bok choy is tender crisp. Return meat and juices to the skillet and stir fry 30-60 seconds until hot.
Place 1 serving of hot rice in a bowl, scoop 1/4 of meat and bok choy over rice. Sprinkle with a few red pepper flakes, to taste. Repeat with the other 3 servings. Traditionally this is a spicy hot dish.