1. Peel and chop up the onion and garlic. Pour some olive oil in a large casserole and place it over medium-high heat. Then add the chopped onion and garlic as soon as the oil is hot.
2. Stir and gently fry the onion and garlic for 5 minutes. Peel the chorizo sausage and cut it into bite-size bits. Add it to the onion in the casserole together with the fresh rosemary.
3. Stir well again and then let the chorizo sausage bake for 3 to 4 minutes until the oil is totally red. Now pour in the drained lentils. Season with a good dash of pepper.
4. Give it all a good stir. Then pour in the chicken stock.
5. Stir well again. Turn the heat high until boiling. Then turn the heat back to medium-low and put a lid on the pan. Simmer the lentil soup for 10 minutes. Right before serving stir in the freshly chopped parsley. Check the seasoning and add extra salt or pepper to taste if necessary. Scoop the soup into bowls and serve.