If you wanted to add a "master power" that will kill power to everything, I would use a double pole double throw (DPDT) or a double pole single throw (DPST) switch rated for 230AC service. One pole breaks the L1 (red in the schematic) line and the other breaks the L2 (black in the schematic) line. You will only use one side of the switch. The reason you want to break both is they are both carrying 115v AC with respect to the neutral and ground. If you only break one leg, it will kill the power to the PID and element, but the other leg will remain hot and if you were to touch it and a ground at the same time you could kill yourself. You would wire (electrically wire, as in insert in the schematic) this switch into the L1 and L2 wires as the first component after the power enters the cabinet (before the L2 115v to the PID splits from the L2 to the other side of the heating element). You will need to ensure the switch is rated for at least 230v and for continuous duty at the maximum amperage the smoker can draw under worst case conditions. Generally the switch will be rated 250v.
This is a schematic of the common types of switches. Either the DPST or DPDT will work for this build (only use 1/2 of the DPDT in essence using it as a DPST).
If you wire a 230v outlet where the smoker is, you can accomplish the same thing by just unplugging the entire smoker. A lot less complex to wire. If you are building a 220v-230v smoker, I would put a 30amp 230v outlet in and just do the unplug thing. Make sure if the smoker is not in a weather protected area like a garage or covered porch that your use an outlet that has proper weather protective coverings.
If you are wanting to do something other than a master power switch to kill everything, let me know what it is you want and I can address that. There is a lot you can do with process control systems, it all depends on how complicated you want to make the wiring.