I only boil the Zucchini and Yellow Squash. I don't feed Cucumber but I guess you boil it as well. I get bags of frozen peas and just defrost them . I also forgot to mention Spinach, Spinach is good as well.
I usually only feed cucumber and other vegetables to plecos, oto's other catfish, snails, and shrimp. On the occasion I feed my goldfish them too. When I had oto's in with guppies, the guppies would occasionaly nibble on it. I wouldnt suggest using it as a staple food.