A Monday without flesh but with dairy, which involves the horrible suffering and death of cows and their babies?
A Monday without flesh but with eggs that involve the killing of all male chicks at birth and the horrible suffering and eventual death of the laying hens (and eggs have a higher rate of animal death per 1000 calories than beef and pork)?
There is no morally coherent distinction between flesh and other animal foods.
If you regard animals as members of the moral community, today is Vegan Monday.
Every day is vegan.
Life is vegan.
We should encourage and help others to go vegan but we should never present anything short of veganism as morally acceptable. We should always make clear that veganism is the only rational response to the recognition that animals count morally.