P Channel mosfet seems to put out the voltage of the MCU input
I built this circuit, exactly, with the exception of the Zener.
  I put 24V on the N Channel's gate
  


Both MOSFETs are irreparably compromised due to excessive voltages between gate and source due to: -


Using a 24 volt supply and removing the zener (damaging the P-channel FET)
Feeding 24 volts to the gate on the N-channel FET


Once damaged, both MOSFETs will conduct in "strange ways" because the gate-source-drain insulation has broken down. Respect the maximum gate-source breakdown voltage of MOSFETs (usually a maximum of 20 volts but can be less).