Pi Zero / GPIO Pins / +12V Power and Sharing Ground
The circuit you show is generally fine. I only have little concerns/recommendations:

Add at least some resistance at GPIO 20 to limit the current required to charge the gate capacity.
I would increase the pulldown resistor at the base. 470 Ohm will result in 7mA, which usually is not needed in such a scenario. I believe, some kOhm would be sufficient and this resistor and the one I recommend in 1. would form a voltage divider, decreasing the gate voltage to some extend.
Evaluate what the 1 Ohm resistor does when it fails (I guess you will use it to ignite the charge). If it fails short the current might exceed the mosfet's rating.