Pour boiling water over mushrooms in a bowl. Cover and let stand 30 minutes or until tender, and drain. Squeeze mushrooms to remove excess moisture. Chop mushrooms.
Heat oil in a medium saucepan over medium-high heat. Add pancetta; cook until crisp. Remove half of pancetta from pan with a slotted spoon, and place in a medium bowl, reserving remaining pancetta and drippings. Add the mushrooms, squash, breadcrumbs, cheese, rind, salt, nutmeg, and egg to bowl, stirring to combine.
Working with 1 won ton wrapper at a time (cover remaining wrappers with a damp towel to keep them from drying), spoon about 1 tablespoon squash mixture into center of each wrapper. Brush edges of wrapper with water, and top with another wrapper, stretching top wrapper slightly to meet edges of bottom wrapper. Press the edges together firmly with fingers, and cut edges with a 2 1/2-inch round cutter. Repeat the procedure with remaining won ton wrappers and squash mixture.
Fill a large Dutch oven with water; bring to a simmer. Add half of ravioli; cook 3 minutes or until done (do not boil). Remove the ravioli with a slotted spoon. Keep warm. Repeat procedure with remaining ravioli.
Reheat remaining pancetta and drippings over medium-low heat; drizzle over ravioli. Sprinkle with sage and pepper.