Method:
Put ginger in a small pot, cover with water and simmer for 10 minutes; drain and discard water.
Put 8 cups water, ginger, port, lemon juice, and sugar into a large pot and bring to a boil, stirring to dissolve sugar. If necessary, cut a thin slice from the bottom of each pear to allow them to stand upright when served, then arrange pears on their sides in the pot. Add more water as necessary to cover pears and simmer, turning occasionally, until tender, 20 to 40 minutes. Using a slotted spoon, gently transfer pears to a bowl.
Boil poaching liquid until reduced and slightly syrupy.
Whisk together mascarpone and orange zest in a bowl. To serve, pour thickened poaching liquid over pears and spoon dollops of mascarpone over the top of each. Serve warm or chilled.