Hilleberg Saivo
It's "for some values of lightweight", but for what it is (i.e., a totally bombproof free standing 3 person tent) it's not overweight.
You need some widgets to pitch the inner on its own but it does do it. It will also pitch all in one (reallygood for that as fast as possible setup you wanted) or just flysheet on its own.
Price is remarkably un-small, as you would expect. If you do get one note it has been re-jigged a bit in the 2011 version to make it a little easier to pitch and to improve the ventilation, with a couple of big porch-vents as well as the chimney vents in the roof the previous version had. I'd either make sure you get a 2011 or negoriate a discount if it's an older one (the pics at Moontrail's site are a 2010 model, but I think it's the outer where they've made all the changes so the inner should still look like, or at least very close to, the one there).
Hillies are, IME, the easiest tents to pitch (excepting pop-ups). They go up fast and easy even if there's just one of you, in mittens.
You note it's for desert use, and the tougher fabrics and zips Hillie use in their Kerlon 1800 range (incl. the Saivo) should do better with wind-blown sand and grit that are more common there.
For my last Hillie I dealt with Alpenstock, who seem to have as good a set of prices as anyone and know the products really well.
Pete.