I googled a few recipes and then, as ever, came up with a few short cuts
30g no added sugar fruit & nut muesli (internet recipes generally said use oats then add dried fruit & nuts, but the supermarket's own muesli has it all!)
6tbsp apple juice (this ended up far too sweet in my opinion and I would use milk, or even water in future)
1 eating apple, grated
1 dessertspoon greek yoghurt with honey (most recipes say plain yoghurt + honey, and I just happened to have this in the fridge for the kids)
I believe the original recipe soaked the muesli in the apple juice (or liquid of your choice) overnight. I forgot so soaked it for about 45 minutes on the kitchen counter whilst I got my disabled daughter dressed, out of bed, and ready for her school bus. Other more modern food writers say as little as 10 minutes soaking is all that is required.
When ready to eat, grate the apple and stir in the yoghurt and tuck in.
My verdict: This is not a quick breakfast. You have to remember to soak the muesli for as long as takes your fancy/schedule. Grating an apple also adds a little more time. And after all that I found it rather too sickly sweet.
I would soak my muesli again - it plumped the fruit up nicely - but I am more likely to soak it in milk as I get my kids ready for school and eat it later when the chaos subsides. And then pick up an apple from the fruit bowl and eat that as I head out.