Umbrian lentils are well-suited to absorb the earthy and salty flavors of this dish. Any type of small dried lentil can be substituted.
Preheat oven to 300 degrees. Heat oil in a Dutch oven or medium ovenproof pot over medium heat. Add vegetables and bacon, and cook until onion is soft and translucent, about 10 minutes. Add lentils, and cook, stirring, for 1 minute. Pour in stock to cover lentils. Bring to a boil. Cover, and transfer to oven. Braise until tender and thickened, about 1 hour. Season with salt and pepper, and drizzle with olive oil.