If you've got a planted tank, you've probably also got a couple of the weight strips laying around somewhere. I've found they're an excellent way to hold veggies to the bottom of the tank. On zuchinni slices I just poke one end thru the slice and bend it over, then stick the other end into the gravel.
Lettuce I just roll up a bit and crimp the strip on.
Peas, however, are a nuisance. I use frozen peas, let them thaw, then nick the outer case and just squeeze out the inner section. Trouble is, too small to fasten to anything, too light to stay put in the tank. The otos' end up pushing them all over the tank, usually under driftwood and into plant stems, and then the snails get too much of it. Still trying to think of a solution for that...I'm guessing pleco's, being more robust, snarf peas nearly whole.