I wanted to know if you can connect 2 pi zero's to 1 spi screen and have a switch to switch between them?
Roughly speaking, SPI displays accept a sequence of configuration commands at startup, followed by display commands afterwards.
Assuming both RPis configure the display in the same way, you may be able to toggle the display which was configured by one of the RPi between two devices. You should only toggle the SPI interface lines, not the power, as any power interruption will likely result in an unconfigured display which will not show anything. You will probably still encounter a few issues down the road:
The RPi which start up without a display may notice its absence and start without any GUI. In that case, you may have to start RPi1 with the display connected, toggle the display to RPi2 and start it in turn, then toggle between RPi1 and RPi2 at will.
Unless you modify the driver, toggling will result in corrupted SPI commands which were being sent at the moment of switchover, and graphical glitches resulting from the sequence of SPI commands from RPi1 being replaced by the sequence from RPi2. Hard to say how bad it will be without trying out.
If the display drivers periodically poll the display and halt/crash when no response is received, toggling will not be possible at all without modifying those drivers.