m0n0wall has a function 'wake on lan' under service for that. You need to access the m0n0wall webgui from the internet (add a WAN rule to allow this for https), then use the GUI function 'Services: Wake on LAN'. Works for me.
I was hoping to get Wake-On-Lan without resorting to logging into the monowall router.
Any other suggestions? Or is this juts not possible with monowall?