Remove the skin and seed of the avocado, then slice it into 5mm thick pieces.

Make a cut in the mentaiko and extract the contents. Reserve a small portion for garnish.

Boil water in a pot and cook the somen noodles according to package instructions. Rinse under cold water and drain well.

In a bowl, mix mentaiko, mayonnaise, milk, and salt and pepper. Add the somen noodles and toss to combine.