Heat the oven to 200c/fan 180c/gas 6. Toss the squash and red pepper in the harissa paste and oil. Spread the chunks out on a large baking tray and roast for 20 mins until softened and the edges of the vegetables are starting to char.
Meanwhile put the Bulghar wheat in a large bowl and pour over the hot stock, then cover tightly with cling film and leave to absorb the liquid for 15 mins until the grains are tender, but still have a little bite. In a separate bowl, mix the garlic and lemon juice into the yogurt and season to taste.
Let the Bulghar wheat cool slightly then toss in the roasted vegetables, chickpeas and spinach – the leaves may wilt a little. Season, if you want, drizzle with the garlicky yogurt and serve warm.