Do you want to feed the fish some plants? <They do love veggies....>
In that case: duck weed is #1 favorite hands down. But they will try pretty much anything if you blanch it first (spinach, lettuce .....)
If you want to have a planted tank & don't want the fish to eat them, you are in for a challenge. Some plants are less likely to be eaten: Java ferns, Anubias, hornwort. However, even these are not foolproof .... They will munch on the leaves from time to time, esp. young leaves. <So if you get a small specimen, it will prob get eaten.> You can maximize your chance of success by having lots of mature/healthy plants to start (so the plants grow faster than the rate of consumption), and to choose less palatable plants that are fast growing.