Oyako-don (chicken and egg over rice)
Cook thinly sliced yellow onion in a broth made of dashi, soy sauce, mirin, sake and sugar. (Let onions simmer until are they are fairly soft and have taken on a light brown hue.) Separate onions and broth.
In a 6-inch non-stick skillet, heat one tablespoon of vegetable oil. Sautee sliced chicken thigh and sliced shiitake mushroom together. While chicken and mushrooms are cooking, crack two eggs in a bowl. Separate out one yolk (optional). Lightly beat the two egg whites and one yolk together. When chicken is just barely cooked through, add scallions (that have been chopped into 2-inch lengths) and dashi broth (about an inch-depth's worth). Pour beaten eggs into skillet. Use a fork to evenly distribute the eggs, cover and let steam about five minutes.
Fill a bowl with cooked rice, top with onions, then gently coax the egg and chicken over the top. Carve out a little hole in the middle and place the reserved egg yolk. Garnish with thinly sliced scallions and shichimi togarashi. Serve with sriracha.