they can eat that very well, it only has barely any nutritional value.
You can try lots of veggies and fruit.
In the amazon it's part of their natural diet, for a lot of those food will fall into the water.
You can try grapes, pieces of pineapple, banana,cantaloupe, wtaer- and sugermelon, just see what they like .
Just don't try Kiwifruit, it will make more then a mess of your tank.
Zuchinni is still all of my big plecos favorites:
and it has loads more nutritional value as well, compared to cucumber, which is mostly water.
And mine is doing fine on a quarter of a zuchnni a dat, that is together with a 8" Pseudacanthicus cactus pleco