We have an epidemic of new build houses around here, all with internal block walls lined with plasterboard fixed by dabs of adhesive.
The new owners of these properties all seem to want large TVs, wall units & mirrors fixed to the walls.
Solution I use, gives a really strong fix & might be useful to others;
Rawlplug 'UNO' brown 7mm plugs. These work well in pretty much any material.
3" x 10 or 4" x 10 Quicksilver screws, depending on thickness of fixture.Assuming its a TV bracket; Mark wall through one fixing hole at top of bracket. Drill 7mm hole. You will most likely drill through the plasterboard, then into the block, simply because a larger area of the board 'doesn't' have adhesive.
Insert plug, place point of screw into plug & give a sharp tap. You will feel the plug enter the block itself. Now offer up bracket & do up screw till almost tight. I do this with a hand held screwdriver, it gives you a better feel for how tight the fixing is.
Level the bracket - much easier now one corner is fixed, mark the wall, swing bracket aside, drill & plug other holes as above.
Should you drill through a dab of adhesive, simply fix as usual.
I've not found a need for spacers.