i stayed at the lms guest house on my recent nairobi visit, and had both breakfast and dinner at the restaurant multiple times.
there was a good amount of vegan dishes, during my stay, not sure if it's always like that? the staff was friendly and helpful, answering my questions about what had animal products, and what didn't.
the food was pretty good, nothing that great. still, i feel it's worth a try.
Cons: not 100% vegan, food is only ok, christian music all the time!!!