Heat olive oil in a large pot or Dutch oven over medium heat.
Add onion, carrots, and celery, sautéing until softened, approximately 7 minutes.
Stir in minced garlic, thyme, and oregano, cooking for 60 seconds until fragrant.
Add rinsed lentils, turkey stock, and diced tomatoes with their juices.
Bring the mixture to a boil, then reduce heat to low, cover, and simmer for 30 minutes or until lentils are tender.
Incorporate the cooked turkey and simmer for an additional 5-10 minutes to ensure the meat is heated through.
Add baby spinach and stir until wilted.
Remove from heat, stir in lemon juice, and season with salt and pepper before serving.