Heat the oil in a large casserole pot. Brown the sausages in batches until brown all over. Remove from the pan, then add the diced onion, celery and carrot and cook for 10 minutes until softened and golden. Add the garlic, chopped tomatoes, beans, paprika, oregano, bay leaves and chicken stock then return the sausages to the pot. Simmer for 45 minutes, until thickened.
Meanwhile, preheat the oven to 180°C/gas mark 6. Cut the tortillas into gravestone and cross shapes, each around 3-4 inches in height, and bake for 8-10 minutes until crisp.
Once the stew has finished cooking, transfer it to a glass baking dish and remove the bay leaves, then sprinkle over the chopped parsley to look like grass. Arrange the tortilla crisps on top and serve.