Preheat the slow cooker to the auto or low setting. Soak the saffron threads in the vegetable stock and set aside. In a large casserole dish, heat the oil and add the onions. Cook slowly for 8 minutes until soft and translucent by keeping the heat low. Add the garlic, ginger and chilli and stir for a further few minutes until fragrant. Transfer to the slow cooker.
In the same large casserole dish, melt the butter then add in the chopped carrots, potatoes and parsnips. Cook for 8 minutes until evenly browned on all sides. Add the coriander seeds, lemon zest and juice, salt and pepper and cinnamon. Transfer to the slow cooker, cover and cook on auto or low for 7 hours. Prior to serving, stir through the olives and remaining fresh herbs.