Saute the onion, garlic, beans, and shallot, and ginger in the dashi for about 5 minutes.
   
 
Step 3:

Add the chicken. About mid-way through cooking the chicken mix the Soy Sauce, mirin, and sugar, and slowly add 1/2 of it too the chicken. BTW, if you want a more yellowy-oyakodon, use a light soy sauce instead and water down the stock a tad (otherwise it'd be too salty). I'm using standard dark soy here.