Lentil and Chorizo Soup

Name: Lentil and Chorizo Soup
Ingredients: 6 tablespoons olive oil; 1 medium leek, cleaned and finely minced; 2 stalks of celery, cleaned and cut into small dice; 3 carrots, cleaned and cut into small dice; 4 cloves garlic, minced; 1 large chorizo, cut into small slices; 1 cup green lentils; 64 ounces chicken stock; 1 whole dry-farmed or roma tomato