Place the mixed vegetables and half the Walnuts in a food processor and pulse to give a coarse paste. Remove the skins from the sausages and mix the meat into the vegetable paste, season. Divid into 20 small balls.
Heat the oil in a large frying pan and fry the meatballs in 2 batches for 5 minutes each until golden, remove and set aside. Add the tomatoes to the pan and fry for 2 minutes, add the grains, remaining Walnuts and spinach and stir until just the spinach has just wilted. Return the meatballs back to the pan, cover and heat through for 2-3 minutes.
Meanwhile, mix the yogurt and mustard together and serve with the stir fry.
