Oyako Donburi literally means "parent-child rice bowl" because it's made with chicken (parent) and egg (child). It's a one bowl meal: fresh steamed rice topped with tender pieces of chicken and onions cooked with egg in a soy based sauce. If you have a family of big eaters, make extra rice.
Trim the fat off of the boneless skinless chicken thighs (if there are any tiny bits of bone, give it a rinse and drain as necessary), cut each thigh into 6-8 pieces, and place into a large bowl
Add onions, scallions, soy sauce, mirin, and sugar and mix; if prepping ahead, cover and refrigerate to marinate 30 minutes or overnight.
Use a large frying pan or a braiser with a lid and heat it up for 1 minute at medium heat.
Crack eggs into a medium mixing bowl and scramble, set aside.
Add chicken into the pan, add dashi or chicken broth, cover with a lid, and cook at medium heat for 5 minutes.
Stir the chicken and add prepared eggs, cover with a lid and simmer on low heat for 5 more minutes. Serve with rice.