Cut the chikuwa in half lengthwise and into bite-sized pieces. Separate the shimeji mushrooms by hand, and thinly slice the onion. Remove the mentaiko from its skin.

Heat salad oil in a frying pan over medium heat. Add the chikuwa, shimeji mushrooms, and onion, and stir-fry until the onion becomes tender.

In a bowl, mix silken tofu, mayonnaise, salt, pepper, and mentaiko until the tofu becomes smooth. Add the stir-fried ingredients and mix well.