
Prep all ingredients: slice shiitake mushrooms into bite-sized pieces, slice onions, beat the eggs. Whisk together dashi (or chicken stock), mirin and soy sauce to make the sauce.
Place a pan over medium high heat. Add oil and then add shiitake mushrooms and sauté until mushrooms start to develop nice colors. Then add sliced onions and sauté until fragrant. Season with salt and black pepper to taste.
Pour the sauce into the pan and let it come to a boil, then reduce heat to a simmer and cook for 45 seconds or so. Add oysters to the pan, evenly distribute them in a single layer. Cover the pan and simmer for a minute.
Remove the lid and drizzle the beaten eggs slowly and evenly over the oysters and mushrooms. Cover the pan again and cook with medium low heat for 1-2 minutes, just until the eggs are still a little runny, silky and moist.
Add cooked rice to serving bowls and top with the oysters, mushrooms and eggs. Sprinkle some sliced scallions and serve immediately.