- I think Vegan is a rare trait so getting the breakthrough 'Gene Selection' could help
- Create a massive colony in an end game state (everything researched, all wonders built)
- I had over 2800 colonists and was on Sol 172 before getting 200 vegans
- You can check how many Vegans you have in the Command Center (hotkey 'Z') and filtering to Quirk: Vegan
- This achievement did not unlock immediately for me when reaching 200 in the Command Center, it unlocked around 2 sols later so I am not sure the exact condition it requires.