Well, there are certain food items which are considered as
Amisha Dravya. They are prohibited to be consumed during Vratas or while performing Purascharana or during Asaucha (birth-death impurity) period or on the day before a fast or other similar times.
And, there are certain food items called
Havisya Dravya which are just the opposite of Amisha and which are fit to be consumed during the aforementioned times.
I have the book "Nitya Karma PujA Paddhati" (similar to the Hindi book Nitya Karma PujA PrakAsh) which describes "Amisha Dravya Nirupanam" (Determination of Amisha substances) as follows:
Meat, fish, betel leaves, onion, garlic, red spinach, a kind of lemon
and all smoked/burnt food items are considered Amisha for Hindu purpose.
Few Havishya Dravyas, on the other hand, are:
Rice (the "Atap" variety). ghee, cow's milk, curd, barley, certain
root vegetables, mango, sugarcane, amlaki, haritaki, banana, red salt
Now, the problem will arise if you translate "Amisha" as non-vegetarian. Clearly, for example, betel leaf is not non-vegetarian by the definition of the English words, but it is still considered as Amisha substance for Hindu purposes.
NOte- This is only a partial answer.