The following assumes you are using a regular small to mid-sized pan. If making more a larger amount of servings, you should split them into (no more than) 2 servings at a time in one pan.If using an Oyakodon pan, servings should be prepared individually. Put the pan on a stove without turning it on.
Add onion slices and distribute evenly. Your pan is the right size for the amount you're cooking if the onions just about fill the pan in a single layer.
Stir the seasoning mixture into the dashi broth and pour into the pan. It should be 100ml per serving in the pan and just about cover the onions.
Turn on the heat to medium and bring it to a simmer.
Add the chicken in an even layer on top of the onions.
Let it simmer uncovered for about 2-3 minutes without stirring.
Stir now to flip the chicken and let simmer for 2-3 longer until the chicken is no longer pink on either side.
Drizzle the egg mixture into the pan, distributing evenly. If you didn't reserve an yolks for the end, hold back some egg mixture now and pour it in later, right before removing the pan from the heat.
Sprinkle with mitsuba (or green onion) and keep simmering.
Take the pan off the stove. The egg on top should still be runny. (If you don't like it too raw, keep simmering for however long you prefer.)
Distribute the rice to the bowls, then slide the chicken and egg mixture on top.
Pour the remaining sauce from the pan over the bowls to your liking.
If you reserved an egg yolk, make a little hole in the middle and add it there.
Sprinkle with some togarashi and serve!