Heat the olive oil in a large pot over medium heat.
Add the chopped onion, carrots, celery, and diced kale stems. Sprinkle in the cumin, salt, and a few grinds of black pepper. Cook for about 8 minutes, stirring occasionally, until the vegetables begin to soften.
Stir in the grated garlic and cook briefly, just until fragrant.
Add the fire-roasted tomatoes, rinsed lentils, white wine vinegar, thyme bundle, and vegetable broth. Stir everything together.
Cover the pot and let the soup simmer for 25 to 30 minutes, until the lentils are tender.
Add the chopped kale leaves and cook for another 5 minutes, until wilted.
Remove the thyme bundle and taste the soup. Adjust seasoning with salt and pepper if needed.
Serve warm, topped with chopped parsley, a pinch of red pepper flakes, and grated Parmesan if you like.