First, blot the beef dry with paper towels.
Peel the yellow onion, garlic, ginger, and kiwi. Chop the kiwi and half of the onion into chunky pieces. Blend the chopped onion and kiwi with the garlic, ginger, soy sauce, sugar, 1 tablespoon of the sesame oil, and the pepper.
Put a layer of beef in a rectangular container and cover it with a generous amount of marinade. Repeat until there's no more beef and marinade left. Cover the container with a lid or plastic wrap and refrigerate for 3 hours.
Cut the remaining half of the onion into thin slices, and cut the green onions into 3-inch pieces. Wash and discard the stems of the shiitake mushrooms and cut them into thin slices.
Heat a pan over high heat with 1 tablespoon of the sesame oil and sauté the beef for a minute, then add the yellow onion, green onion, and shiitake mushrooms and sauté for a few more minutes, until all the ingredients are cooked.
Serve it over freshly cooked rice and sprinkle toasted sesame seeds and thinly sliced green onions on top for garnish!