Heat a pot with oil over medium heat. Add the onions, ancho, and garlic. Cook until the onion begins to soften. Add the pumpkin, sage, water, and cream. Bring to a boil and simmer until the pumpkin is completely soft. Transfer the pumpkin mix to a blender. Add salt and pepper and blend until smooth. Put the sauce back into a pot and bring to a simmer. Toss with the cooked pasta. Season the pasta with salt and lime juice to taste. Divide the pasta between 4 plates. Add the cooked shrimp and garnish with the shaved manchego.