What you are asking is to "resaw" this into more usable lumber. This comes with some challenges:
- It's ~20 inches in diameter, which is pretty large.
- It's urban lumber, and no one wants to risk hitting a nail with their expensive saw that can resaw 20 inches.
There are a few ways you can resaw this, and one requires finding someone with lumberyard equipment willing to risk hitting a nail. There is equipment intended to cut slabs that might be able to slice this lumber (essentially a high-powered horizontal band saw), but it isn't common in the home shop. You'd have to call around at local lumberyards and ask if they resaw small jobs of urban lumber. Some places specialize in resawing urban lumber so you might get lucky.
I suppose a large enough band saw that had a large enough throat could do it, but that would be a really big band saw. And then you'd have to hold the lumber in a pretty dangerous jig. And then you might still hit a nail. So, you need to find someone with a 24in band saw who is willing to put in the time to jig this up safely and risk breaking a blade. You'd be expected to cover the cost of the blade, I expect.
If you have a good friend and some patience you can try to resaw this the old fashioned way: with a "two-man" saw (otherwise known as a "misery whip") but that would take some dedication and a lot of sweat equity on your part. And you'd have to buy or borrow the saw, and know how to use it.
Put plainly: you need to find someone with special equipment willing to do this work and take the risks, or you have to do the work yourself.
Be aware that cross-sections like this are very unstable the thinner you make them. It'll start to check and crack, and there will not be anything you can do to stop it. This is why large blocks like this are usually quite thick.
Honestly, you should do what everyone does who has a large cross section like this as a chopping block: put it somewhere semi-permanent and don't move it. A board like this is intended to be used in a more commercial setting, as it can take a lot of abuse and be scraped down as it wears. Find a place for it in the kitchen prep area and live with it.