Your question isn't as clear as it might seem. Firstly, what do you mean by "ticket"? Are you looking for a bug, issue, or defect tracking system? Or some other kind of ticket (e.g. change tracking, service orders, etc.)?

I assume "should run as CGI" is a result of not being allowed to install Apache modules/etc. on the target server? "should run as... php" doesn't make sense (PHP is like Perl in that it can run either as CGI or using a web server module {i.e. mod_php}).

You'll have to come up with a better definition of "simple": do you mean "simple to manage", "simple code", "simple design", "simple to use"?

Do you really mean "should rely on MySQL", or do you mean "must be able to use MySQL if it needs a database"?

Depending on your answers to these questions, I have a couple of suggestions:

1. Bugzilla - very powerful, proven, out-of-the-box bug and issue tracking system.
2. Eventnum - MySQL's issue tracking product.
3. Trac - source control and issue tracking package.