Sepp has one thing you don't: 100 acres.
He can toss his seed everywhere and wander around to harvest.
He also has 70 ponds and little creeks between the ponds. While a lettuce plant in the sun will die in august, the same kind of lettuce is probably doing pretty good right next to the
water.
Plus, a pile of rocks in the sun, about ten feet away from a bunch of tap
root trees/bushes/annuals (or a
pond, or creek) will effectively water whatever is around it through the summer (water will condense on the stones under the stack)
In Seattle, there is a lot of cement and bare roofs.
Mulch helps a lot. But in Seattle, mulch attracts slugs, pill bugs, rove beetles, symphylans, etc. All of these can be mitigated.
I think the best thing to do is to start with anything. Grow stuff. Try to use as little water as possible. Mulch with stones and branches, and leaves and any
yard waste. But I would still water once in a while.