As most sci-fi fans know, science fiction really took off as a genre in the late 40s with the likes of Asimov, Heinlein etc.
Most of these authors were terrible writers, but they were ex scientists with good imaginations whose intriguiging stories more then made up for "character development" being an unknown concept to these men.
Interestingly, despite being scientists when these authors wrote about a future where meat was hard to come by they imagined that people would live off of texturized yeast.
I guess they never took a trip out of the country or to an ethnic restaurant
I read an interesting trilogy a few years ago by Kim Stanley-Robinson. He is a modern day member of the Heinlein/Asimov's ilk, but in addition to being an ex-scientist, he knows how to write, he knows politics and slightly left of center.
The future he projects in Red Mars is projected from the 1990s, not the 1950s so it hits closer to home and is more interesting.
Of course, the world is over populated. The meals in the book are vegetarian without going out of their way to mention it, though at one point in the book it is mentioned that most people live off of tofu, fish and rice.
The big veg reference in sci-fi I always really liked was the planet of the vegans in classic Star Trek, partly because it was unintentional. The crew of the Enterprise goes to collect the bodies of colonists who were mistakenly placed on a planet with lethal solar radiation.
To their surprise they find the colonists alive, some in better health then before they left. Everyone is suspicious. Spock asks how they survive on a planet with no animal life and the leader proudly proclaims that they are all vegetarians ( vegans -- no animals, no milk, eggs etc ).
It turns out that a narcotic like plant keeps them all alive, but that is another post.
So, what are some of the interesting references to vegetarianism that you have found in sci-fi?