Cut a butternut squash in half lengthways, place it upside down on a baking tray/sheet and bake on 180 degrees for about 20 - 30 minutes. Eat as is with a good dollop of butter mushed in, or scrape out of the skin and mash in a bowl with said butter and a little salt if required. Yum. Nice with a sprinkle of coriander mixed in too.
Failing that, why bother with the potato at all? There is no substitute in low-carb. Anything potato-like is going to be starchy, so it won't be low-carb.
You have to try and overturn your entrenched habits with this. We get programmed to think that it can't be a proper dinner without potato. Not true of course, but its all about reprogramming and breaking the habits. Cereal for breakfast, biscuits with the coffee, potatoes/rice/pasta with the dinner. Pudding, snacks, chocolate, crisps, etc., etc.
If we lived somewhere where none of these foods were eaten, we wouldn't miss them!
You won't starve. Honest........