Mould on wall (that backs onto kitchen cooker)

There is a patch of damp/mould on my sitting room wall.
It is in the corner, exactly where the kitchen cooker would back onto the wall from the next room.
I assume that's the problem- but is there anything I can do to solve it? There's an air vent in the sitting room, on the outside wall of the house.

I'm pretty clueless about this kind of thing, so if I need to get someone out to look at it, who do I get? A builder/plumber??


Thanks for any suggestions.