But surely there should be a QRH or an OEB to advise me?
With an engine shut down ECAM has advised you to "MONITOR FUEL IMBALANCE" (implying "carry out the FUEL IMBALANCE procedure if required). Old ECAM standard requests FUEL X-FEED OPEN. As MB2002 points out this is a more serious problem than the fuel level and those actions take precedence.. think of FUEL LEAK which says "do not open crossfeed even if requested by another procedure" .. ECAM can be wrong! Pilots are paid to be right, not to follow blindly the wrong move because the book says so.
Every other aircraft I've flown had a Low Fuel Contents procedure which ensured all the fuel was available to all my engines - even when Engine Out.
As does the A320 when OEI - but when on two engines Airbus choose to isolate them in a low fuel situation for reasons best known to themselves.
To expand on
Abnormals are written for one failure/caution/warning only
if you write a procedure for every possible combination of faults the cockpit really would be full of manuals without room for a pilot...