drag and drop in correct order

My suggestion:

1. Add a STATE to each of your correct items called INVISIBLE (except for ONION, skip that one).  After you create this state, delete the image from the state so the state exists, but has nothing in it.   Then set INVISIBLE as the beginning state for all your food except onion.
2. Now paste a new copy of the same food images back over the originals in the exact same spots.  Name each one of these new ones as tomatoBAD, LettuceBAD, etc.
3. Add each of these BAD images to your Form View list of DRAG ITEMS, but do not assign them a Drop Target.
4. Under Drag & Drop Options, set the "Return item to start point if dropped outside: a correct drop target"
5. Last step is to set two triggers on each of the CORRECT items, starting with Onion.
   • Change state of TOMATO to Normal when Onion is dropped on top loaf
   • Change state of TomatoBAD to HIDDEN when Onion is dropped on top loaf.
6. I also added a SUBMIT trigger when the bottom loaf is dropped on the top loaf so the interaction completes automatically.

See what we've done?  The only droppable item that is visible initially is the onion.  All the others are fakes ones that are always wrong and will snap back if you try to use them.  Once you drop the onion, you reveal the next real one and hide it's corresponding BAD version that was on top of it.  Visually no one can see that happen, but it works!