You can go to allrecipes dot com to find the recipe by ingredient. When you get to the page, put your cursor over the "more searches" don't click a menu will automatically drop down, then you click on "search by ingredients" button. Then you can type in ingredients you know the cake has, you can even type in ingredients you don't want in it. There is also a keywords bar under it you can enter associated words "garbage cake" or "dump cake". There are a few variations of dump cake most recipes contain pineapple and cherries, but it is called dump cake because you just dump in a few ingredients and viola you've got cake some people are as bold as baking it right in their pyrex bowl, not that I recommend it, and I have never tried it but some people do it.  Some Garbage cake recipes that I have found are close or identical to dump cake, still with most recipes containing crushed pineapple and pudding mix. There could be a chance that your Grandma added her own personal flare and added the orange zest in herself. 

Hi   Now this is Orange zest   the gratings from the orange to add the estential oils  right? Now  suppose the fact that Dump cake comes to mind -- a dump cake is an old boy/girl scout camping concept  one dumps a can of pie filling say cherry  into a dutch oven then you dump a box of cake mix then the eggs if called for  and then put the lid on the dutch oven put coals on top and let it bake  near the campfire

If you consider doing a search for a dump cake and the process sounds familiar then simply add the orange zest  or maybe grandma used orange juice as the liquid  of course the ease of combining the ingredients for a Dump cake has taken the dessert into a modern day kitchen --  however,   if it is the Orange cake you seek there are no doubt plenty of recipes for  whipped topping  mandaian orange segment cake that has a moniker which causes a fair amount of tittering and chuckles when the baker announces to the guests the cake name which is a pronouncement ,to some of a  extremely  personal nature--- regarding  an activity one does not necessarily discuss in public

Hi angeleyes, If you haven't gotten a recipe by now,, Here's the one for "Dump Cake":1 can crushed pineapple,1 can cherry pie filling,1 box yellow cake mix,2 sticks margarine. Mix together pineapple,pie filling,and pour into bottom of a 9"x13" baking pan,pour dry cake mix on top, cut up the 2 sticks of margarine into thinslice and put on top. Bake at 350 for 55-60 min.  Another recipe is almost the same, except you start with the pineapple and add everything in layers with 1c. chopped nuts. Thats the one my daughter-in-law makes. Your Grandmother may of just added orange to it. I couldn't find a recipe for the 'garbage cake". Try it and let us know what you think

 It is such an easy cake here it is. This is a good summer cake.
Preheat oven to 350 degrees F.
Prepare 13X9 pan, greaseed.
1 Can (19 ounce) cruched pineapple, with juice
1 Can (19 ounce) cherry pie filling
1 yellow cake mix (18.25 ounce)
1 Cup coarsely chopped almonds.  (I have used pecans)
2/3 Cup butter, cut into thin slices.
Dump pineapple with juice into pan.  Spread evenly.  Spoon pie filling evenly over top.  Sprinkle cake mix evenly over the fruit.  Sprinkle nuts over cake mix.  Put butter pats over nuts, covering as much as possible.
Bake for 45-55 minutes or until golden.  Serve warm or cool.
I have played with other pie fillings and cake mixes, spice with apple pie filling.  Carrot cake mix and I used coconut (that was a long time ago, don't remember seeing carrot cake mix in a long time.) I think the newer coconut or pineapple cake mixes would be good.
I make one in the fall with  pumpkin pie filling on the bottom rather than the fruit.  That is soooo good.  I like it better than pumpkin pie!

Thank you, My Mother-inlaw makes this but never gave out the recipe. I like that you have spelled out the recipe for everyone to understand.