In a small saucepan, combine the sugar substitute, cornstarch, nutmeg and cinnamon; stir in water until smooth. Add 2 cups peaches. Bring to a boil over medium heat; cook and stir for 2 minutes or until thickened. Cool to room temperature.
In a blender, process 1/2 cup peach mixture until smooth. In a large bowl, whisk milk and pudding mix for 2 minutes or until slightly thickened. Let stand for 2 minutes or until soft-set. Stir in pureed peach mixture.
Spoon remaining peach mixture into tart shells; top with pudding mixture. Refrigerate until set. Cut remaining peaches into small pieces and arrange on top.