In a heavy 5 to 6-quart kettle, combine the sliced rhubarb, lemon juice, grated lemon peel, sugar, and ginger; let stand for 4 hours.
Bring mixture to a boil over medium-high heat; cook, stirring often, for 10 to 15 minutes, or until a jelly thermometer registers 220° or use the cold saucer test.
Stir in the nuts and simmer for 1 minute, stirring.
Ladle the conserve into hot sterilized jars; seal. Jars can be refrigerated for up to 2 months, or freeze for up to 1 year.
For longer storage, this conserve must be processed in a hot-water bath for 10 minutes. Store in a cool, dark place.