In the series debut of 'The Sarah Jane Adventures' (which I watched while on vacation - Syfy was having a marathon.), Mrs. Wormwood of the Bane used her mental powers to read Kelsey's mind. Not that there was much to peruse: Mrs. Wormwood thought she worshipped the "Holy Oak". And then she realized the young girl was thinking of 'Hollyoaks'.
This doesn't have to be a Zonk. There was no mention of the TV soap opera, so Hollyoaks could be anything in Toobworld.
Luckily, there are relatively few mentions of it as being a pop culture reference in other shows:
'The Thick of It'
- Malcolm tells Hugh that Simon Hewitt will be photoshopping the show's extras by the end of the month.
So it is a TV show then, but not the one we know in the real world.
'Gavin And Stacey'
- Pam says the tension between Gavin and Stacey "is like living in Hollyoaks."
I'm thinking this could mean it was a show like 'Big Brother' - each week, the people in Hollyoaks (perhaps an estate?) would go at each other's throats before somebody is finally voted out.
But at least the actual soap opera can be considered a real part of the TV Universe!