Combine zest, sugar, vinegar, ginger, cinnamon sticks, peppercorns and salt in a large non-aluminium saucepan. Simmer, stirring to dissolve sugar, for 5 minutes. Add the pumpkin. Simmer, stirring occasionally, until crisp-tender, about 15 minutes.
Transfer pumpkin pickles to sterilised jars, using a slotted spoon. You will need 8 x 250 ml jars or 4 x 500 ml jars. Pour in cooking liquid to within 5 mm of the top of each jar. Seal. Refrigerate and use within 1 week.