hi
for peas,lettuce (use romaine or kos lettuce iceberg is too fibrous) cucumber, courgette (zucchini) i put the item in boiling water for around 15mins or zap in microw for a few secs, let cool then put in tank (you can buy a suction thingy with a clip to hold the lettuce & cucmber etc) for peas you need to pop them out of their outer skin after zapping & then i mush them up & chuck them in. all out fish love this stuff even our pakistani loaches will snaffle mouthfulls of the lettuce.
be careful with giving other stuff like cheese, although fish will go bonkers for it its not good for them as apparently they cannot digest it & it could cause serious problems.
ive seen our lfs put small bits of raw potato in the tanks but our mob are not impressed with it. havent tried banana - must give it a go.