Step 1Place the meat in a large saucepan or small Dutch oven with the unpeeled onion, unpeeled garlic, half of the peppercorns and 2 teaspoons of salt. Add water to cover by about 1 inch. Bring to a boil over high heat; at once reduce the heat to maintain a low rolling boil and skim off any froth that rises to the surface. Cook, partly covered, until tender, 45 minutes. Lift the meat into a bowl, letting it drain very well. Strain the stock back into it. You should have about 3 to 4 cups.
Step 2Bring 1 cup of water to a boil in a small saucepan. Add the dried chiles and cook, uncovered, until softened, about 5 minutes. Drain and set aside.
Step 3Cut the unpeeled pumpkin into 8 equal-size chunks, removing any seeds and strings. Add it to the stock, along with water--if needed--to completely cover the pumpkin, and bring to a boil over high heat. Reduce the heat to maintain a low rolling boil and cook until tender, about 30 minutes. Lift out the chunks of pumpkin. Place in a colander to drain well, and let cool to room temperature. Reserve about 1 cup of stock.
Step 4Scrape the flesh of the pumpkin from the skin and into a bowl; discard the skin. Mash thoroughly with a potato masher or pestle. Set aside.
Step 5Place the pumpkin seeds in a small, heavy skillet over medium-low heat. Toast, stirring and shaking the pan, until they begin to swell up and pop, about 3 to 5 minutes. Set aside.
Step 6Grind the coriander seeds and remaining 1/2 teaspoon of peppercorns in an electric coffee or spice grinder or a mortar and pestle until finely ground. Coarsely chop the remaining onion and garlic; puree in a blender with the pumpkin seeds, ground spices, chopped tomatoes and chiles.
Step 7In a medium-sized saucepan, heat 2 tablespoons of the lard to rippling over medium-high heat. Add the pureed mixture, reduce the heat to medium, and cook, covered, stirring occasionally, until the fat starts to separate, about 10 minutes. Add the reserved mashed pumpkin and the vinegar, stirring to mix well, and cook, covered, for 10 minutes. Taste for salt and add more to taste, up to about 1 teaspoon.
Step 8While the pumpkin mixture cooks, heat the remaining 1 tablespoon of lard in a large skillet. Add the meat and brown lightly for about 5 minutes, letting it get a little crisp but not dried out.
Step 9Spoon out the seasoned pumpkin onto a platter and top with the meat.