This is the traditional verse for recitation to express repentance:
忏悔文
Verse for Repentance
往昔所造诸恶业
For all the evil deeds I have done in the past
皆由无始贪嗔痴
from beginningless greed, hatred and delusion
从身语意之所生
created by my body, speech and mind
今对佛前求忏悔
I now before the Buddha, express regret and repentance
However, I’ve come across fellow Buddhists whom at times,
are uncertain of what to repent about,
which made me think of coming up with an extra more specific version.
忏悔文（素食版）
Verse for Repentance (Vegetarian Version)
往昔所食诸众生
For all the animals I have eaten in the past
皆由无始贪心吃 (吃 puns with 痴; delusion)
from beginningless greed (and delusion)
从身口意之所生 (口 puns with the eating mouth; not just speech)
created by my body, speech and mind (actions, words and thoughts about eating animals)
今对佛前求忏悔
I now before the Buddha, express regret and repentance
The truth is, even if you are a vegan now,
you are likely to have ate many animals in your past (lives)!
This makes the verse a universal one!
May this verse also urge animal-eaters to reflect on changing to a kinder diet.