I made a simplified oyakodon last night. Chicken stock, soy & mirin simmered, add thinly sliced chicken breast and sliced scallions, bring back to a simmer, add a few beaten eggs, let them set and serve over rice. When I was growing up my mom used to make katsu donburi with a recipe she got from our Japanese expat neighbors -- much more time consuming and authentic but this was still delicious and took only about 20 minutes, since we already had cooked rice.