Heat the olive oil in a large saucepan over medium heat until shimmering, about 3 minutes. Add the celery, carrot, and onion and cook, stirring occasionally, until the vegetables have softened, about 10 minutes. Stir in the garlic and cook until fragrant, about 1 minute. Season with several generous pinches of salt and pepper.
Add the vegetable broth, tomatoes with their juices, lentils, bay leaf, and thyme and stir to combine. Cover and bring to a simmer. Can take 15-30 minutes.
Once simmering, reduce the heat to low and continue simmering, covered, until the lentils and vegetables are soft.
Taste and season with more salt and pepper as needed, then stir in the red wine or sherry vinegar. Add the spinach and stir until wilted.
For a creamier texture, you can purée half of the soup in a blender and add it back to the pot.
Once the soup is almost done, add in the cumin, chicken bouillon and cayenne pepper (or your pepper of choice).
These seasonings give it a unique twist and make the soup super awesome!
Note: The original recipe came from this website. However, I changed it a bit and added my own seasonings and now it's my favorite lentil recipe.