Bring 6 cups of water and 1 teaspoon of the salt to a boil in a large pot.
Rinse the barley in a strainer under cold water.
Add the barley to the pot, stir, and bring back to a simmer.
Cook uncovered for 40 minutes, stirring occasionally.
Add the currants and cook 5 minutes longer, or until the barley is very tender and the liquid is absorbed.
Transfer the barley and currants to a large bowl and add the olive oil. Allow the mixture to cool at room temperature for 30 minutes, stirring a few times.
While the barley cools, trim a small portion from the bottoms of the peppers so that they will sit flat.
Slice the tops to create "lids" and remove the membranes and seeds from inside the peppers.
Place the hollowed peppers in a deep baking dish and sprinkle the insides with the remaining 1 teaspoon of salt.
Zest the lemon using a zester or a grater. Cut the zested lemon in half and juice it.
Add the lemon zest and juice, walnuts, feta, scallions, and black pepper to the cooled barley mixture.
Preheat the oven to 400 F.
Divide the barley filling between the peppers.
Replace the lids.
Pour the wine around the peppers in the dish.
Cover the dish and bake the peppers for 40 minutes.
Uncover the dish and bake 5 minutes longer.
Remove the peppers from the oven.
Take off the pepper lids and spoon any pan juices over the filling.
Garnish the filling with the parsley, and serve immediately.