Without context, it's hard to give you a precise answer. "Ham" can refer to an actor who really draws attention to himself by overacting. "Bread" can mean money. If you provide the full sentences where you heard these alternate usages, it would help.

Yes, big difference. One goes inside the sandwich and the other goes outside the sandwich. Can guess which goes where?

When in doubt, stay with traditional speech. It is safe. Contrary to what you might hear, slang is not so popular. It is more often used by less educated individuals. Very unfortunate but true. Proper and formal language usage will always get you more respect.

I agree with Susan612. I don't see how they can mean the same thing. "Ham" is more of a colloquialism than slang. I'm sure it's in the dictionary. It can mean a bad actor in a theatre. It can also mean an amateur, as opposed to a professional. In particular it can mean an amateur radio enthusiast--people who operate radio transmitters on specially set-aside "ham bands" just for the joy of playing with the technology. Offhand I don't know any slang meaning for "bread" other than "money." I assume there's a connection with "dough." I think of "bread" as OUTDATED slang from the 1960s era, by the way.