I feed lots of zucchini squash, green bean, sweet potatoes to my plecos....what I do is slice it in about quarter inch slices an drop it in boiling water for about 3 min-it usually will start to sink by that time.I remove it from the hot water to cold water to stop the cooking and to cool off so that I can remove the seeds.
Once cool and seedless I drop it in the tank...If it doesn't sink I will stick a fork in it to keep it on the bottom.
For cucumbers-I make quarter inch slices, remove the seeds-stick a fork in it to keep it under water-remover every 24h
Spinach-I do a 20-30 second blanch on it-then drop in cold water-once cool I place it in the tank with a rock on top of it.
For 1 pleco-I would feed half an algae wafer every other day and offer a protein meal once a week too-like a shrimp pellet.
If you feed fresh blanched veggies-offer small amount to start and remove and replace every 24h.
I never have to remove anything-between the plecos, shrimp and snails its all gone within 12h.