Mix the cake mix, water, oil, and eggs together, as directed on the cake mix box. Bake the cake in a 13 x 9" baking dish, using the temperature & time suggested on the cake mix box. Remove from oven and cool.
Drain the pineapple well. (I actually squish it with a wooden spoon, just a little, so the cake won't get soggy.)
Spread drained pinepple over the cooled cake.
In a blender (or using a bowl & mixer), mix together the cream cheese, pudding mix, and milk until well-blended. Pour over the pineapple on the cake...
...and smooth the pudding evenly over the cake.
Refrigerate at least 30 minutes until the pudding is set. Then frost with Cool Whip.
Refrigerate again until ready to serve. (If there are any leftovers, refrigerate them, too.)
I wish this photo showed the whole slice of cake. Silly JAP editing! =^..^=