Lettuce
lettuce
There is no single answer. Tomatoes and lettuce, for instance, along with some other fruits and vegetables, are not sold frozen.
I'm not positive, but I've never seen canned or frozen cucumbers:)
watermelon
Lettuce
Tables
Lettuce
Lettuce
Lettuce
I have never seen eggplant in a processed form.
The first commercially available frozen vegetable was spinach or peas.
The likely answer is watermelon. However, there are commercially available dried watermelon chips, and these can be made at home (although they may have limited shelf life). Pickled watermelon rind is also sold in some areas.