Sprinkle Growmore, chicken pellets, or whatever you've got to hand over the mulch, then 'tickle it in' as best you can using a fork or rake. That should help most of it find its way to the soil surface - just need to wait for rain then to wash it in (did I really say that?
)
You could liquid feed of course, but I tend to use that as a quick fix much later in the season than this.
Glad you're on the mend Londongardener - don't overreach yourself, your health and vitality is much more important than your plants'.