Preheat oven to 220°C / 425°F.
Chop all the vegetables and the fish, juice the lemon and get everything ready to cook.
Boil the potatoes in salted water for a couple of minutes.
Add the 2 eggs and set a timer for 8 minutes. Remove when ready, then plunge into cold water to cool. Peel and cut into quarters, setting aside.
In a separate pan, fry the onion, carrot, and celery in olive oil for about 5 minutes, then add the cream and bring to a boil. Add the spinach leaves and Dijon, and stir to wilt.
Place the fish into an appropriately sized oven dish and add the chopped parsley, lemon juice, grated cheese, and mustard. Pour over the vegetables and cream, and mix. Arrange the quartered eggs evenly across the mixture, pressing them in.
When the potatoes are cooked, drain them in a colander, mash them with the butter, and season with salt, pepper, and grated nutmeg. Spread over the top of the fish mixture.
You can drizzle a bit more oil or melted butter over the top to get a browner finish or sprinkle over more cheese if you really want to be decadent and get a crisper top.
Bake for about 25 - 30 mins - until golden.
Serve with heated baked beans in tomato sauce and blanched green beans (or other green vegetables/salad of your choice)