How do you hang a gate on a twisted post?

You can use the type of hinge that is a screw threaded bolt that the gate sits on. You would just have to drill the pilot holes in the right place and angle. If using a strap hinge, you can either shim behind one or chisel out a groove for the hinge to sit in. Without seeing it, it's hard to give specifics on how to do it. Set the gate in the opening and see what it takes to make the hinges you want to use work.