Warm a pan for 1 min. Add the pearl barley. Toast over a medium heat, stirring now and then, for 2-3 mins till the barley smells nutty and has picked up a little colour. Tip into a bowl. Take the pan off the heat.
Peel and finely chop the onion and carrot. Put the pan back on the heat. Add ½ tbsp oil and the chopped veg. Season. Cover. Sweat over a low heat for 10 mins till softened.
Meanwhile, halve the squash. Scoop out the seeds and peel it. Chop into chunks around 1cm across. Tip the barley back into the pan. Add the squash and most of the thyme. Crumble in the stock cube. Pour in 800ml boiling water (or use homemade stock).
Cover, turn the heat up and bring to the boil. Turn the heat down and simmer for 20 mins till the squash and barley are tender.
Tip the pumpkin seeds into a dry frying pan. Toast over a medium heat for 2-3 mins till the seeds are a little browned.
Fish the thyme sprigs out of the soup. Taste and season. Ladle into bowls. Scatter over the pumpkin seeds and a few fresh thyme leaves to serve.