It can be done with one pax agent, but only if the right facilities are available and the agent is clued up and on the ball. My previous experience of EZY at STN is that neither of these things are happening.
I have seen/done plenty of non-fiddled, genuine 20 min turnarounds and I know it can be done, although the classic 20 min turnaround chart from easyjet is a load of old cobblers - network analysis at its worst.