This article is from the Vegetarianism FAQ, by firstname.lastname@example.org (Michael Traub) with numerous contributions by others.
Unfortunately there is no simple answer to this. Many Companies
allow individual stores to decide part of their menu, or the
ingredients used. In general, you should:
1. Ask for a nutrition information booklet. Asking an employee may
not be enough.
2. If the food in question contains an undesired element, ask if
it can be substituted for, or deleted altogether.
3. Fill out a comment card, if you think their menu does not have
enough selection. If the company receives enough of these, they
may decide to follow up on them.
4. Taco-Bell do not use lard anymore in their cooking.