Combine peach nectar and sugar in a saucepan over medium-high heat; cook, stirring often, until sugar dissolves. Remove from heat; stir in lemon juice. Pour mixture into a 13 x 9-inch baking dish; cover and freeze 8 hours or until firm.
Remove mixture from freezer; scrape entire mixture with a fork until fluffy. Serve immediately, or store in a covered container in freezer.