Heat the oil in a frying pan over a medium heat. Fry the onion with the cumin seeds, smoked sweet paprika and cinnamon for 4-5 minutes, until starting to soften.
Put the squash, cauliflower and spiced onions in the base of the slow cooker and sprinkle over the red rice, red quinoa, buckwheat and pearl barley. Add the stock, cover and cook on low for 3 hours.
Wilt the spinach in the microwave and stir through the grains with the chopped mint. Season the grains with black pepper and divide between 6 bowls. Sprinkle with crumbled cheese and a squeeze of sriracha to serve.