My low sugar diet also means low carb, as the starch and glucose in potatoes raises your blood sugar, so I've been looking for some good alternatives. I like cauliflower and wondered if I could make a fish pie and put mashed cauli on top, and found a few recipes online doing just that.
I followed this recipe for the cauliflower puree but I couldn't get mine smooth enough; I think if I had cooked the cauli for longer so it was softer that might have been better. I wouldn't have thought to add cheese and cream into it as well; it was quite nice, though to be honest I would have preferred mashed potato!
For the fish pie, I cooked a mixture of fish - I think I had white fish, salmon and smoked mackerel, and added some chopped leaks and made a white sauce.
I put it in a pie dish, spread the cauliflower mash over the top and popped it in the oven to brown.
Here you can see the fish and the topping. This felt like a very virtuous recipe and is good if you're cutting down on potatoes and miss having fish pie - but I have to say I would only eat it as "diet food", whereas a lot of the low cal/fat/sugar recipes I make are nice enough to eat whether you are on a diet or not.