Many means more than one or two and hence always precedes plural countable nouns:
I have many friends. - She has read many books.
So many help, many money, many pizza and many tortilla are all ungrammatical.
On the other hand, lots of can mean both a large amount of and a large number of. In the first case it is followed by a singular noun, and in the second case by a plural noun:
(Note, however, that lots of, particularly when followed by a singular noun, is considered very informal.)
The complication is that many nouns, particularly food nouns such as pizza, may either be conceived of as referring to the entity/food itself or to separate instances of that entity/food. In the first case the singular noun is used, and in the second case the plural noun.
So, I eat lots of pizza has an emphasis on the total amount of pizza eaten, whereas I eat lots of pizzas places greater emphasis on the number of individual pizzas.
As for tortillas, I can only speculate that lots of tortilla does not sound right because a tortilla is conceived solely as an individual item. So, I eat lots of tortilla sounds as odd as saying I eat lots of grape. Maybe someone has a better idea.