can I just go get some clear plastic and solarize the beds to kill it off?

Yes, until the stolons make their way into your beds again. That is: you need to kill the grass outside the beds as well, and keep it away.

Dan

I don't really want to kill the grass outside the bed. I guess if it is a problem I'll just solarize it once a year in the spring; since zoysia is slow to spread more than a few inches. Or I could just add a barrier to the one edge of the beds that isn't more than 3 inches below the soil line.

I'd do a barrier, as you don't want to kill any beneficial critters in the soil.

Dan