Dissolve Jell-O in boiling water. Add cold liquid (water and juice off pineapple). Let set until Jell-O begins to thicken.
Stir lemon pie filling or prepared and cooled lemon pudding into thickened Jell-O with an electric mixer. Reserve one cup of mixture. To the remainder at the crushed pineapple. Put into 13x9 pan and refrigerate till set.
Whip Dream Whip as directed and fold in the cup of reserved Jell-O mixture. Spread over first layer and refrigerate.