I feed zuccini to my plecs, the platys, swords, & danios nibble on it too. Peas, lettuce, cucumbers, and carrots are also some of the things I've fed them. Just be sure to rinse them real good, some may have pesticide or other residue.
Lightly cooked and deshelled peas are popular. Took three times before my swordtails decided that they liked them, now they go into a frenzy when I give them peas.
Carrots were boiled a little, the rest went in as is. With zuke & cucumber, remove the seeds first. They make a real mess if you don't. I found out the hard way. Yuk!
With the peas I use frozen peas and microwave them for about 1 1/2 minutes in a small amount of water. Let them cool (run under cold water if your in a hurry) and then pop the insides out of the shell. Throw the shells away and mush up what you have left. Then just drop it in the tank. If they don't seem interested you'll want to remove it from the tank after a few hours. Like I said, the first 2 times they didn't want anything to do with it but the third time they went nuts for it!