The important thing here is the "Lee Evans arranges" bit.
The arrangements *are* easy, there are no tenths in the left hand or lightning fast runs in the right and they fit the hand nicely.
The harmonies are not extreme, they are simple but not "simplistic". In other words everything is standard but carefully harmonized for maximum effect with minimum notes.
Here's an example from Nightingale sang in Berkerly Square: the cadence of the title phrase: bars 9 and 10:
1Maj7 V1 11 1V-V7 1
(followed by a single bar of sort of AMaj-BMaj-Ab-Bb magic that links back to the start of the theme (in Eb) - all done with single notes in the base and single or double notes in the RH)
Then it takes off with "classic-melodic-standard" Lee Evans development that any professional would be glad to play in a cocktail bar (meant in a good sense - I like this sort of thing) before finally returning to the last cadence in from 5th bar from the end but this time he *varies* the left hand to this:-
RH (same as above)
bar (end - 5) all quater notes in block chords
next bar first two beats 8th notes, last beat 8th notes (Bb is last note)
next (last three) bar(s)
Eb arpeggio etc to end.