I didn't bother with the topping because we had whipped cream on hand. I also forgot to pick up the evaporated milk and just used 1% milk. It was just fine. Really great mocha flavor. Easy too. Will make again.
The pie itself is wonderful. But the topping leaves something to be desired. The tang from the Greek yogurt is a bit too much. I'll make this again, but will likely just top the pie with fat-free whipped cream with a bit of coffee mixed in.