
In a non-stick frying pan or cast iron skillet over medium high heat, add the dashi stock, soy sauce, mirin, and sugar. Bring to a boil.
Add the chicken, and simmer in the stock for 10 minutes. Spread the sliced onion over the chicken and cook for 2 minutes.
Pour the beaten egg over the top, and simmer, covered for 2-3 minutes, until cooked but slightly runny.
Serve over freshly steamed rice and garnish with chopped scallions.