Have you tried serving them in water? Leaving them with the ducks overnight? Smushing them up? Letting the ducks see another duck eat them?
Just ideas. My ducks will eat ANYTHING... but sometimes it takes them a day or two to warm up to it. One time I served them diced bell pepper and they tasted it, shook their heads and spit it out. Then they waddled away, muttering curses at me. LOL But the next morning, it was gone without a trace!
I grow mesclun greens for them. The drakes won't touch them, they prefer weeds. The hens love the greens. Guess I have hens that prefer gourmet food, and drakes that prefer burgers and fries! Put them in water, that may help. Otherwise, maybe they just don't like peas! I have tried cabbage (they love it), lettuce (they won't eat it), apples (won't touch it), carrots (a few if they are really small), cataloupe (even pureed it - they wouldn't touch it). They prefer to harvest their own weeds.....
Now mine are so crazy about lettuce, one of them jumps for it if I hold it high enough. I've tried putting them in water, leaving them in their pen, the whole 9 yards. They just don't like them and it's probably a case of a little money see, monkey do as well.
My adult ducks had never had peas till this year when i saw everyone was feeding peas to their ducks, when I put them in a bowl No way would they eat them but i started putting them in their pool and boy do they like to dunk for peas, My little duckling loves them of course he started on them as a baby.
My four 4 week old babies LOVE them....they almost take off fingers. I have literally had the tip of my fingers in their mouths many, many times. And, that fatty part of my ring finger right above my ring and just under the knuckle.....oh, it gets nibbled on like crazy....have to pull my hand away to get it out of their mouths. Feeding my babies peas? It is one of my VERY favorite things to do. And, I have just barely...two days ago....started putting it in their pool....LOVE it....not only they love it, but I love watching them.