Preheat the oven to 200C/180C fan/gas 6 and grease a large roasting tray.
Put the squash and half the thyme onto the tray, then scatter over half the olive oil and season well with salt and black pepper. Place in the oven to roast for 10-15 minutes until just golden brown.
Meanwhile, bring a large pan of salted water to the boil. Add the pearl barley and return to a simmer, cook for 25 minutes then drain and set aside.
Heat a large sauté pan until hot, add the remaining olive oil, onion and garlic and sweat for 5 minutes until just tender.
Add the drained pearl barley and stir well. Add the white wine and cook for a couple of minutes until it has evaporated.
Add the vegetable stock and bring to a simmer then cook for 25 minutes until totally tender and the liquid has evaporated.
Stir in the parmesan, baby spinach and roasted squash and heat through until the spinach has wilted. Check the seasoning and serve with a green salad.