Make the nagaimo sauce. Put the grated nagaimo in a bowl and mix with the egg, mayonnaise, salt, and pepper.
Remove the hard part of the asparagus and cut into 4 cm pieces. Discard the root ends of the shimeji mushrooms and shred. Thinly slice the onions.
Flake the mackerel in a gratin dish with the juices.
Top with Step 2 asparagus, shimeji mushrooms, and onions.
Top with the Step 1 nagaimo sauce and bake in an oven or oven toaster at 230°C for 15~20 minutes.
This is the tofu sauce version Recipe ID: 2419088
Story Behind this Recipe
Canned mackerel is a great for those who are dieting, so I added nagaimo to bulk it up for this gratin dish.
You don't need to pre-cook the ingredients, so it's easy to make. You can replace the nagaimo with other vegetables if you like, but the onions will remove the smell of the mackerel and give a boost of flavor! You can use canned tuna, add rice to make doria, or use just vegetables!