1. 1. Saute the aromatics: In a large skillet over medium heat, warm the olive oil. Add the chopped onion, carrots, and celery. Cook for 5-7 minutes, stirring occasionally, until the vegetables begin to soften. Stir in the minced garlic and cook for another minute until fragrant.

2. 2. Combine in the slow cooker: Transfer the sauteed vegetables to your slow cooker. Add the rinsed lentils, vegetable broth, diced tomatoes (with their liquid), dried oregano, dried thyme, black pepper, and salt. Stir everything gently to combine.

3. 3. Slow cook to perfection: Cover the slow cooker and cook on low for 4-6 hours or on high for 2-3 hours, or until the lentils are tender. The cooking time can vary slightly depending on your slow cooker and the type of lentils used.

4. 4. Add the greens: About 15-20 minutes before serving, stir in the fresh spinach. Replace the lid and allow the spinach to wilt into the hot soup. It will reduce significantly in volume.

5. 5. Brighten with lemon: Once the spinach has wilted, stir in the fresh lemon juice. Taste the soup and adjust seasonings if necessary, adding more salt, pepper, or lemon juice to your preference.

6. 6. Serve and enjoy: Ladle the hot soup into bowls. Garnish with a fresh lemon wedge, if desired, for an extra burst of citrus.