Clean the pumpkin by removing the seeds and the rind: you should get about 12 oz. of clean pulp, which you will cut into cubes. Slice the leeks into 1 cm round slices. Peel the potatoes and turnips, and cut them into cubes, like the pumpkin. Prepare a bouquet garni wrapping all the herbs around the slice of pancetta and tying them with kitchen string. Heat 2 tablespoons of oil in a large pot, brown the bouquet gently, then add all the vegetables. Let cook for 1 minute, then cover with 1.5 quarts of water. Bring to a boil, lower the heat and simmer for at least 1 hour without stirring to avoid breaking up the vegetables. Towards the end of the cooking, season with salt. Cut the bread into irregular pieces, sprinkle it with grated Grana Padano cheese and toast it in the oven. Serve the soup, finished with a drizzle of oil and accompanied by the toasted bread.