I have a single gang outlet, can Plugzio be installed on top of that?

Absolutely. Plugzio is designed to be retrofitted.

This type of an outlet is fairly common in parking garages:

Here are the instructions on a possible way to install Plugzio on a single gang outlet.

Step 1: Remove the existing outlet from the box (make sure the breaker is OFF)

Step 2: Place it on top of the two gang box and mark the standard hole punches on the back of the  2-gang box.

Step 3: Drill the existing screw holes inside the two-gang box.

Step 4: Align the two-gang box with the existing hole on the single box and screw it in.

Step 5: Finish installing Plugzio