Heat the oil in a large pan. Add the onions and cook over low heat, stirring occasionally, for 5 minutes, until softened. Add the pumpkin, bacon, and nutmeg, stir well; then cover and simmer, stirring occasionally, for 5-8 minutes. Pour in the basic vegetable stock, increase the heat to medium, and bring to a boil. Reduce the heat and simmer for 10-15 minutes.
Meanwhile, make the bacon croutons. Heat the oil in a skillet. Add the bacon and fry for 4-6 minutes on each side, until crisp and all the fat has been released. Meanwhile, cut the bread into ½-inch squares. Remove the bacon squares and cook, turning and tossing until golden brown all over. Remove from the pan and drain on paper towels. Remove the pan from the heat and let cool slightly.
Transfer the soup to a food processor or blender, in batches, if necessary, and process until smooth. Return the rinsed-out pan, season to taste with salt and pepper, and reheat gently, stirring occasionally. Remove the soup from the heat and ladle into warm bowls. Sprinkle with the croutons, crumble the bacon over the bowls, and serve immediately.