Make sure your Oreo crust is chilled if you made it from scratch. Let the ice cream sit at room temperature until you're able to stir it, but it's not all the way melted (about 10-15 minutes). Stir the macadamia nuts into the ice cream. Pile the ice cream into the pie, then freeze until hardened, at least 1 hour.
Spread the hot fudge over the top of the frozen pie. Sprinkle with more macadamia nuts. Freeze for at least 4 hours or overnight.
To serve, top with whipped cream. It's easier to slice if you let it sit at room temperature for about 10 minutes. The first slice might be messy!