From an actual historical perspective, the little i know, it seems like the vegetarians in the 1800 west side world (Like Europe and the US) used a lot more of the whole vegetables compared to what we are used to today, i also think they had a lot of farmers old cooking, like mashed turnips, may beets, mashed potatoes and cabbageroots (are they realy called Swedes in English?) (that side dish is called "rotmos" (mashed roots) in swedish, my mother used to make it with boiled meet, but i think people ate it as it is if they did not had meat in season) etc.
If we exclude butter, which mid class and poor farmers usualy had to do anyway, it's still edibly just a bit dull and watery taste but still enough energy to, live on.
Another thing is bark bread (but that was normaly more limited to the very north), the real thing obviously does not use bark, but the inner cambium layer, dried and mortled mixed with rye floor.
Cabbage sup and bread seem to hawe been very popular among all people since it was relativly sheap but still taste good (for some reason i love cabbage soup my self, my father used to make cabbage soup whan mother was't at home, he started by making broath, then let the cabbage boil properly and just a pinch of salt).
Nettles can also be cooked with only water.
Potatoes and leek soap.
mushroom sauce.
The truth is that most mid class and poor farmers probably ate vegetables most of the years since meat and butter was expensive,at least in sweden all butter where sold on the merket, it was not a thing You could usualy keep. Meat was only a short period in the autumn or reserved in the winter for hard labour.
It was only Soldiers and sailours, etc who had daily meat in ther ransons because of the extreme work they often had to do.
Later forest workers had to add meat/fish and fat (and a lot of carbon hydrates, like rye bread, hardtacks, etc) into their daily diet for the same reason.
Regular farmers could usualy not afford that diet ower the whole year.
