In a large pot or Dutch oven, heat a bit of olive oil over medium-high heat. Add the turkey and cook until browned, breaking it apart with a spoon as it cooks.
Add the chopped onion, carrots, and celery to the pot. Cook until the vegetables are softened, about 5 minutes. Add minced garlic and cook for an additional 1-2 minutes. Stir in the seasonings and mix well to combine
Pour in the chicken or vegetable broth, water, and undrained diced tomatoes. Bring the mixture to a boil. Add the rinsed lentils to the pot. Reduce the heat to low, cover, and simmer for about 25-30 minutes or until the lentils are tender. Stir in the chopped spinach and let it wilt into the soup.
Notes
Transfer leftover soup into airtight container. Store in the refrigerator for 3-4 days. Or freeze for up to 3 months.