Heat olive oil in a large pot or Dutch oven over medium heat.

Add onion, carrots, and celery. Sauté for 8-10 minutes until the vegetables are soft and the onion is translucent.

Stir in minced garlic, thyme, and oregano, and cook for 1 minute until fragrant.

Add the diced tomatoes, rinsed lentils, vegetable broth, and bay leaf to the pot.

Bring the mixture to a boil, then reduce the heat to low, cover, and simmer for 30-40 minutes, or until the lentils are tender.

Stir occasionally to prevent sticking.

Remove the bay leaf and stir in the chopped spinach or kale until wilted.

Stir in the red wine vinegar (if using) for a touch of brightness.

Taste and adjust salt and pepper as needed.

For a creamier soup, use an immersion blender to blend about 1/4 of the soup. Serve hot, garnished with fresh parsley.