Basically, get a small onion, bunches of mint and cilantro, respectively, 3 big mangoes, a red pepper, and mix them up in a bowl. Cube the fruit, julienne the pepper, and chop the leaves of the herbs coarsely. Chop the onion, too.
In a separate bowl, mix together a few ts salt, 1/4 c whey, 1/2 c lime juice and 1/2 c water.
Put the fruit mixture into a quart mason jar, punch it down with something like a meat hammer or a ladle. Add the liquid, adding enough water to fill to 1" above the fruit. If anything floats to the top, try to push it down.
Seal it up and keep it in a warm place for 2 days, then refrigerate.
The trick here is that almost anything blended with whey and left to ferment tastes great. So, for a small jar of mustard, relish or whatever gets a few tablespoons and a quart gets 1/4 cup.