Prep time: 20 minutes
Cook time: 2 1/2 hours
Heat oil in a large shallow pot over medium-high heat. Add lamb and onion and cook for 5 minutes to brown, stirring occasionally. Add garlic and cook for 1 minute more. Stir in pumpkin, beans, broth, tomatoes, chiles, and spices and bring to a boil. Reduce heat and simmer, covered, for 2 hours. Stir in sweet potato and cook for 20 minutes more or until sweet potato is tender. Season with salt. Ladle into bowls and top with sour cream and cilantro, if desired.
While stew is cooking, preheat oven to 400°F and line a baking sheet with foil. Brush lightly with oil. Cut the stems off the pumpkins cut each pumpkin in half to form 4 round “bowls”. Scrape out seeds (a melon baller works well for this). Place cut side down on baking sheet and roast for 30 minutes or until the pumpkin is very tender, but still holds its shape. Turn cut side up and place back on baking sheet. Fill with equal amounts of stew and cook for 15 minutes more. Scrape some of the cooked pumpkin with each bite of stew.