You can make your own - basically an egg salad with watercress. Start with fresh and flavourful watercress. It's fairly easy to grow. This is from my garden.
Boil up a few eggs.
To get nice eggs like this, add eggs to cold water, bring to a boil and let sit covered for 10 minutes. Then chill in ice water before peeling.
Rather then tedious chopping, I simply smash them through a German potato grater. Available from Amazon: Kuchenprofi Potato Grater/Shredder in 18/10 Stainless Steel
Season and add mayo as you like. Personally, I hate mayo so I use Ranch salad dressing. It's got all the seasonings mixed in. It may need a bit more salt, depending on your tastes.
Lastly, stir in the cress:
I spread it on made-from-scratch flat ciabatta bread, but the Britts serve it on something lighter.