Start this recipe by lining a spring-form 22cm cake tin with nonstick baking paper and brush liberally with a tablespoon of butter substitute. Next, mix together the ricotta, eggs and parley and season well with salt and pepper. Put aside while you prepare the filling. Heat the remaining tablespoon of butter substitute in a pan and brown the chorizo sausage for 3 minutes. Add in the spring onions and diced pepper and cook for 4 minutes. Tip this mixture into the ricotta mixture, along with the diced tomatoes. Mix together well then carefully spoon into the prepared tin. Smooth out, then scatter over the sliced red onion followed by the crumbled feta cheese. Bake in the oven for approximately 40-45 minutes at 200`c. Allow to sit in the tin for 5 minutes before removing. Can be served hot or cold.