macOS Launching X11, xterm with command

Does anyone know a way to launch Apple's X11, and then tell the xterm that shows up to run a command? I have the equivalent working for Terminal.app (via NSTask), but I really need to be able to do the same thing for X11. I'm not opposed to kludgy solutions, but so far I've come up with nothing.

Thanks, but I guess I wasn't being clear. I meant how to programmaticly do that in Cocoa, but no worries, I've got it working now.