Pre-heat oven to 190 degrees C.
Remove florets from the cauliflower and steam over boiling water until tender.
Place the cooked cauliflower, one tablespoon of butter, 2 tablespoons of the cream, salt and pepper in a food processor and blend until smooth. Set aside.
In a large frypan, melt butter and fry of onions and carrots over a gentle heat until soft. Then add spinach, the remainder of the cream, mustard and bring to a simmer. Taste for seasoning. Remove from heat and add chopped herbs.
In a large lasagne dish, arrange your chunks of fish and hard boiled eggs. Pour over your cream and vegetables.
Carefully spread your cauliflower over the top and then top that with the cheese.
Bake in the oven until the cheese is melted.