No, I'm not going to say it.
Anyways, the Oasis challenge is an aboveground challenge, although certain exceptions are allowed and encouraged.
Here's the setup: find a desert that has an aquifer. Settle there. Now, carve out a semi-smooth (i.e., ramps in some places, but sheer cliffs in others) circle down to the aquifer layer, with a slight cratering (circle gets smaller the farther down). Once you reach the aquifer, channel out roughly one third (or smaller) of the circle and get it to fill up with water.
Now, survive off the oasis. Active farming is not recommended, but it's fine if you want to. Instead, food is to be acquired by hunting/husbandry and flooding the bottom layer of the oasis to make it muddy, and then harvesting the plants that show up automatically. I'm not sure if muddied surface ground will yield more wild plants than otherwise, but it's worth finding out.
Housing and other important buildings can either be built outside or carved out of the side of the rings. Please note that each digging operation should only be one or two rooms deep into the sand. No grand hallways branching off into elaboraste underground structures. Treat the side of the oasis crater as the front wall, and dig out the rest of the house or storeroom behind it.
That's all that comes to mind right now. It looks a bit muddled, but I haven't found a better way of describing it yet. Maybe later.