Heat oil in a dutch oven over medium heat. Add chopped onion and 1 teaspoon of sea salt. Saute the onions until they're translucent (5 minutes). Next, add the garlic. Stir for one minute.
Then add the celery, carrots, chicken, bay leaf and oregano. Saute, mixing occasionally for 10 minutes
Add the lentils, chicken stock and another teaspoon of sea salt. Bring to a boil and let simmer for 45 minutes with the lid slightly ajar. During the last five minutes of cooking, stir in the parsley.
Once the lentils are fully cooked, turn off the heat. Stir in apple cider vinegar and season with pepper.