Line a lipped tray or shallow container with baking paper.
Add the plums and sugar to a saucepan set over a medium heat.
Simmer for about 5 minutes until the fruit has broken down and a syrupy sauce has formed. Transfer it to a bowl and set in the fridge until cool.
Using a palette knife, spatula or large spoon, spread the yoghurt in a thin layer (roughly 1cm thick) onto the prepared tray.
Sprinkle evenly with granola and dot pieces of plum all over. Drizzle some of the sauce on top as well.
Carefully pop the tray in the freezer and leave for 2-3 hours until firm.
Remove from the freezer and either cut or snap into smaller pieces, then serve!