how to run a cable in a solid wall

Hello Forum,
How to run a cable in a solid inner wall made of masonry with cavities?

-first I had to use 25 mm sockets boxes otherwise I hit the cavity in the block, which make my life hell connecting cables in the box

-second I used oval conduits because they are very thin (12 mm or less) but they are very difficult to keep in place when I cement them.. should I use self adhesive trunking like
Tower Self Adhesive Mini Trunking 25mm x 16mm x 2m (64026) or else? What's the best practice of running cables in (old sixities) thin masonry blocks with cavities?

Many thanks