Blocking this up

[Jupiter01]

I'm looking for a simple fix to this please. It's a hole left by some plumbing alterations in one of the cupboards. It's quite a tight space.
I have some plasterboard and am used to using the tape and easifill to smooth things out. Struggling to see how I can get a flush finish on this. I would appreciate your advice.

 

[Jurassicspark]

You can use plasterboard and finish it with one coat.

I'd use thermalite block if I was you.

 

[Jupiter01]

Could I stick plasterboard directly on to some of the exposed brick at the too right and left corner and then glue some battens at the bottom to screw in to?

 

[Jupiter01]

Had another thought - could I stick one of those bricks at the bottom and then mount the bottom edge of the plasterboard to that and the top corners already have some exposed bricks. Perhaps I can get a tube of Stixall to fix the brick and then the plasterboard to the bricks too?

I can then tape the edges and easifill to smooth it all in.

 

[Koolpc]

Do it properly. Brick it up. Wont take long and then skim...

 

[Jupiter01]

Do it properly. Brick it up. Wont take long and then skim...

I've never skimmed. Plasterboard and easifill is the closest I have got.
Should I block up and then plasterboard perhaps?