Place a large pot over medium heat. Add 1 tablespoon olive oil and sear chicken on both sides until golden brown, 5 to 8 minutes each. Transfer chicken onto a plate. 

Add onions and celery into the pot and saute until translucent. Add tomatoes and cook until most of the liquid evaporates, about 15 minutes. 

Add seared chicken back into the pot and add the chickpeas and lentils. Add ½ teaspoon turmeric, 1 teaspoon ground black pepper, 2 teaspoons kosher salt and liquid. Stir well and bring the soup to a boil. Reduce heat to medium low and cover the pot with a lid slightly ajar. Cook on a gentle simmer for about 1 hour and 30 minutes to 2 hours.

Mix the flour with 1-2 tablespoons water in a cup until smooth. Add to soup and mix well. Add parsley and cilantro into the soup. Cook for another 30 minutes until the soup is a silky consistency.

Add lemon juice into the soup and cook for another 5 to 10 minutes.

Serve hot.