When MOSFETs get hot, that usually means the gate voltage is too low. It looks like your driving the MOSFET gate through a resistor voltage divider. It would be

When MOSFETs get hot, that usually means the gate voltage is too low. It looks like your driving the MOSFET gate through a resistor voltage divider. It would be better to drive the gate straight from the PI's GPIO pin. Also a flyback protection diode would be a very good idea.