Rig up heavy shade, keep the soil moist and cool, and cross your fingers. But IME with 4 days that hot the odds of success are fairly slim.

Dave

If you have lawn chairs or lounges that are made of slatted or otherwise partially solid material (Ie, it has holes or areas where light gets through, you can kind of set them over the greens. They'll get some sun, just not all of it. That's a lazy man's shade cloth. You could also try real shade cloth.

With temperatures hitting 25°C and up and lots of sun hitting them, I shaded my own lettuce and spinach with a leftover piece of inexpensive wooden trellis, the kind that is often used to close-off the area under a deck. I can easily lean it on the south side of the raised bed's opened cold-frame during the hottest part of the day. Just find a way to have it stay in place and stand up to wind. Still, only so much can be done, but I'm also hoping to get a bit more out of my leafy cold weather crops. Good luck!

is it the same for broccoli and cauliflowers? or they more forgiving? I am planning to shade them and cool off periodically using sprinkles.