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.
Photograph by Antonis Achilleos
Courtesy of Food Network Magazine