Heat oil in a large Dutch oven on medium high heat. Add the onions and cook until they get soft and translucent, 8-10 minutes.
Add the garlic, cumin, and chipotle, and cook, stirring about a minute.
Add the pumpkin, chicken broth, oregano, and salt. Bring to a slight boil, reduce the heat, and simmer for about 20 minutes.
Test to be sure the onions are soft, then use carefully pour the soup into the jar of a blender. You might have to work in batches, depending on the size of your blender. Alternatively, you can use a stick blender right in the pot.
Return the soup to the pot to simmer. Add the lime juice, and taste for seasonings.
Served with lime wedges, and thinned sour cream.