unlikely to be breeze if less than 50 years old. More likely lightweight foamed concrete. Pink plaster is modern gypsum.
It looks to be like the plaster has come off and the block is undamaged.
Easiest and most economical way would be to buy the smallest pack of plaster you can find, mix up a cupful (only as it sets very fast) as stiff as cakemix, press it, hard, into the hole with a metal filling knife, press or scrape it, or use a damp sponge, so the surface is about 6mm below the surface of the surrounding wall, leave it a overnight to set (it may shrink and crack a bit). The next day mix up a smaller amount, as thick as custard, apply it with a broad knife that spans across the hole and presses on the smooth flat old plaster each side (this will level it). Press very hard. Use the knife to scrape off any protruding excess while it is still cheesy. After 20 minutes spray it with water and polish the surface with your broad knife, pressing hard.
You might be able to buy a bad as small as a bag of flour.
A nbig bag is a lot cheaper than you think but sheds dust, and has to be used within a month or so as it is liable to go off and be difficult to use.
Easyplast or joint cement are easy to use but more expensive. To get a smooth finish you must use two coats, the thin topcoat can polish up smooth. Thick coats you will find sink and crack, so you put a thin coat on top, which will polish up smooth.
If you want to take longer for a worse result, you can use decorator's filler.