Combine the pork, beer, 3 cups water and 2 teaspoons salt in a large pot and bring to a simmer over medium heat, skimming the foam off the surface. Add the chipotles and 1 1/2 teaspoons oregano, cover and cook about 30 minutes.
Mix 3 tablespoons pumpkin, the sour cream and salt to taste in a bowl; cover and chill.
Heat the vegetable oil in a skillet over medium heat. Add the tomatoes, poblano, onions and 2 teaspoons salt; cook until soft, 15 minutes. Add the remaining 1 1/2 teaspoons oregano, the chili powder and garlic; cook 5 minutes. Add the remaining pumpkin and cook 5 minutes.
Add the tomato mixture to the pork and simmer until the meat is tender, about 30 minutes. Add the greens and cook 10 more minutes. Season with salt. Ladle the chili into bowls; top with the pumpkin cream and more chili powder. Serve with lime wedges.