Pierce each sweet potato with a fork in a few spots. Arrange on a microwave-safe plate and microwave until soft, about 12 minutes.
Meanwhile, cook the pancetta in a large skillet over medium heat, turning once, until crisp, about 4 minutes. Remove from the skillet and drain on paper towels. Increase the heat to medium high; add the broccoli rabe and 1/4 teaspoon salt to the skillet and cook, stirring occasionally, about 3 minutes. Add the mushrooms, garlic and red pepper flakes and cook, stirring occasionally, until the vegetables are tender, about 3 more minutes.
Mix the ricotta, parmesan, and nutmeg to taste in a small bowl. Split open the sweet potatoes lengthwise and fluff the flesh with a fork. Top each with about 1 teaspoon of the ricotta mixture, then top evenly with the broccoli rabe mixture and the remaining ricotta mixture. Chop the pancetta and sprinkle evenly on top.