TOGGLE/ hollow wall anchor/ wall plug

From Bunnings: http://www.bunnings.com.au/our-range/building-hardware/screw-bolts-fixings/wall-floor-anchors/hollow-wall

This is probably the best: http://www.bunnings.com.au/ramset-8-x-64mm-zinc-alloy-toggle-with-screw-2-pack_p2264715   (Ramset 8 x 64mm Zinc Alloy Toggle With Screw – 2 Pack)