Cook the spaghetti according to package instructions, adding 1 tbsp of coarse salt to the boiling water.

Blanch the lettuce leaves briefly in boiling water and drain.

Cut the enoki mushrooms and avocado into bite-sized pieces.

Prepare the mentaiko mayo sauce by mixing mentaiko, mayonnaise, and soy sauce in a bowl.

Cook the thinly sliced pork belly in boiling water until fully cooked, then drain.

Combine the cooked spaghetti, lettuce, enoki mushrooms, avocado, pork belly, and mentaiko mayo sauce in a large bowl.