So I looked online for some inspiration and found an interesting recipe on BBC Good Food, from which I developed this fast day friendly version. Using cauliflower on top of the spinach and fish turns this into a complete meal.
Choosing a strongly flavoured cheese like parmesan means that you can use a lot less but get a fantastic flavour.
This got the thumbs up from us both and I will definitely be making it again!
For a vegetarian version, you could use smoked tofu, which would have a similar balance of flavours. But I also think that it would be lovely with a couple of big mushrooms each and maybe some chopped walnuts in the topping and some extra cheese.