I forgot to get him to go over the recipe with me last night, but he says he knows how to make it...

I did find this online, but I don't think that's what you meant:

Thai Green Mango with Sweet Fish Sauce, "Mamuang Nampla Wan"

Ingredients
10 green mangoes
1 lb palm sugar
1/4 cup water
1/4 cup fish sauce
1/2 cup chopped shallots
1/2 cup dried shrimp, ground up in a food processor or pounded in a mortar and pestle
2 finely sliced hot chile peppers

Method
Mix palm sugar, water and fish sauce in a pot and simmer over low heat, stirring constantly. When the mixture has become a thick syrup, add the shallots. Cook until shallots are tender. Remove from heat and blend in dried shrmp & chile peppers. Stir well, and set aside

Peel the mangoes and cut into thin slices (approx 1/4", but be careful not to cut them too thin). Place the mango slices in a container and chill in the fridge to improve flavor and crispiness.

Serving
Put mango on a serving tray with the sauce on the side. Dip mango slices into the sauce, eat and enjoy!

You can almost always find green papaya (and mangoes) at Battambang Market on 339 Eddy (near Jones).

Here is a great recipe that I have made many times -- it's quite spicy though so if you want something cooler cut the amount of chilies in half:
thaifoodandtravel.com/recipes...enp.html