Heat olive oil in a large stock pot or dutch oven to medium heat.
Saute onions for 5 minutes until soft and translucent. Add in the carrot, celery, garlic, salt and thyme and saute for 2 minutes. Add chicken broth, lentils and bay leaves and bring to a boil. Lower to a simmer and cook for 20 - 25 minutes, until lentils are softened.
Remove from heat and add in spinach and lemon juice. Disgard bay leaves prior to serving.
Recipe by Good Thyme Kitchen at https://www.goodthymekitchen.com/red-lentil-soup-lemon-thyme/