Heat oil in a pan. Add chicken and fry about 10 minutes, turning once. Season with salt and pepper and let cool. Slice lemon. Rinse and trim leek. Peel carrot. Cut both leeks and carrot into thin strips.
Rinse, trim and thinly slice celery. Heat chicken stock in a saucepan. Add leek, carrot, celery and lemon slices and simmer 5 minutes over low heat. Season with salt and pepper. Remove lemon slices. Cover and let cool a few minutes, then remove cover and let cool completely.
Blanch tomatoes for a few seconds. Peel, quarter, core and cut tomatoes into cubes. Cut chicken into thin slices or strips. Add diced tomatoes and chicken to Consommé and serve garnished with parsley.