You understand wrong. Ham is a noble meat. Only, lesser luncheon meats can be indicted.
The problem is that you made a informed, knowing, and voluntary plea and that's hard to reversed. Lack of probable cause was something that needed to be challenged long ago.
The only times such pleas and convictions are typically overturned is when the defense can show that there was some unconstitutional level of coercion applied to the defendant to get him to plea.
Even then, it's not a guarantee.
You've not provided a shred of detail here that would make it possible to even guess at your chances.
Your other option is expungement:
https://mdcourts.gov/legalhelp/expungement
And you will get better answers here if you don't vent your spleen other people's threads who are trying to get real answers.