What do I fill a "larger" void in a hollow block exterior wall with?

[CrazyFin]

I have had someone come to make holes for ventilation and AC in my home-tech-lab.

Unfortunately, one of the holes (despite several measurements and checks!) was made about 5 centimeters in the wrong direction.
The technician solved it by widening the hole with a new hole next to it, and now I will be able to install a spiral duct that will fit correctly (there is a PVC pipe in the picture below, but it will be replaced with a spiral duct).



The outer wall consists of 10 cm polystyrene blocks with a thin plaster, then about 26 cm thick leca blocks, and on that, there are 13-14 mm thick plasterboards glued directly onto the leca blocks.

What is the most suitable way to fill and insulate the above gap?

I will then glue on new plasterboard to later fill and repaint. However, I am unsure of which method and material are best to fill the gap because the technician had to "widen" the hole.

 

[larsbj]

Foam sealant is probably the best option. Cut away the plasterboard a bit onto the lecan so that the new plasterboard piece is glued onto the leca blocks.