Filling Breize Block holes/Electrical Cables

[StumpedCanary]

Ok, sorry this may be a simple question - I have brieze block walls (I live abroad) and have had a new wall light fitted and while trying to find the electric cable now have 2 deep holes in the block. I've read the advise to use a batten but cannot here as there are no gaps, can I just keep adding filler, letting it dry, adding again until it's flush to the wall (@3.5" deep)? Also have 2 openings where the cables are, what adhesive would I use to bond with brieze block (using the batten technique)? Help appreciated!

 

[StumpedCanary]

I think I am adding a note to my original request for help... am sorry it was such an unexciting topic but surprised no-one offered any advice. That said have found out it is possible to use cardboard to block back of hole without danger of fire from electrical cables which will be behind it.... however if anyone hears of apartment fire in Canary Islands, feel free to wonder!