Heat the oil in your largest saucepan. Add the onions, apples and celery with a pinch of salt. Cook for 10 mins, stirring now and then, until softened. Add the butternut squash, curry powder, cinnamon, nigella seeds and a grind of black pepper. Cook for 2 mins more, then stir in the tomatoes and stock. Cover with a lid and simmer for 15 mins.
By now the vegetables should be tender but not mushy. Stir in the rice, pop the lid back on and simmer for another 12 mins until the rice is cooked through. Taste and add more seasoning if needed. Stir through the parsley and mango chutney, then serve in bowls with yogurt and extra mango chutney on top, if you like.