Heat the oil in a large dutch oven or soup pot over medium high heat. Add the onion, carrot, celery, 2 teaspoon of salt, and 1 teaspoon of pepper. Stir to combine and saute 10 minutes, stirring occasionally, until the vegetables are softened.
Add the garlic and the lentils. Saute 2 minutes, stirring constantly, until the garlic is fragrant and the lentils are lightly toasted.
Add the vegetable stock, water, pumpkin, and herbs. Stir to combine.
Bring to a boil. Reduce heat to a simmer. Cover and simmer for 20 minutes, or until the lentils are cooked to your liking.
Remove from the heat and let sit 5 minutes to thicken slightly. Remove the herb sprigs. Taste and season with salt and pepper to your desired seasoning. You may need quite a bit of salt depending on your vegetable stock.