Persevere with the vegies, I don't actually think they know that it is food at first. Most LFS's don't bother putting fresh food in their tanks.
When I first started putting in zucchini or cucumber none of my fish went near it, but after a few times they worked it out and love it, as soon as I put it in now the BN is there first munching away and defending it till it's had enough, then the other fish get to have some!
Don't leave cucumber in for too long either, it'll make the tank go very cloudy really quicly. The zucchini will as well but takes heaps longer.
Cook peas for a few seconds in the microwave, de-shell them, moosh them up a bit and put them in.
As for the potato, I now have a question to add! Do you cook it first or put it in raw?