Cut the tops off the pumpkins. With a large spoon, remove the pulp and seeds. Discard the seeds or reserve for roasting, if desired. Reserve the pulp. In a small pot, combine the pulp and 1/2 cup water and bring to a boil. Lower the heat to medium-low and cook for about 15 minutes, stirring. Remove from the heat. Carefully, puree the pulp in a blender or food processor. Set aside.
Heat 2 tablespoons of the olive oil in a large skillet. Cook the lamb over medium-high heat, until the lamb is lightly browned, about 7-8 minutes. Set aside.
In a large pot, heat the remaining olive oil over low heat. Add the garlic, onion, cabbage, chili powder and tomato paste and cook for about 6-8 minutes, stirring occasionally. Increase the heat to medium-high and add the lamb, tomatoes, pumpkin puree, rosemary, thyme, and water. Season with salt and pepper and bring to a boil. Lower the heat and bring to a simmer. Cook for about 45-55 minutes.
Preheat the oven to 375°F. Divide the soup into the pumpkins and cover with the lids. Place in the oven and cook for 1 hour. Remove from the oven.
Carefully, transfer the pumpkins to individual plates. Remove the lids and sprinkle the mint over the top. Serve immediately.