I currently have a 12" circular floroscent fixture in the cneter of the kitchen

Plaster and wood lath? Not easily, the lath and plaster loosen when you cut into it. You can put metal
'buttons' all around to hold it in place and then put some joint compound or spackle over it, but it still tends to crack and sag. So you might just remove lath straight across, joist to joist, and shim a little to the thickness of some drywall, tape it and compound it. It will look different unless you are really good at it.

Is your fixture recessed or surface? If this sounds too much, they make some pretty nice hanging kitchen lights. Easier, and cheaper bulbs. Or track lights.