Combine barley and water in a medium saucepan with a pinch of salt. Bring to a boil. Cover, reduce heat, and simmer 50–60 minutes, until liquid is absorbed. Cool.

Preheat oven to 400º. Place a frying pan over medium-high heat. Add olive oil, nutmeg, cayenne pepper, 1/2 teaspoon salt, and spinach. Toss to coat spinach evenly. Add pine nuts and mix again. Cook until wilted, about 3 minutes. Remove from heat; cool.

In a large bowl, combine spinach mixture with cooked barley, remaining 1/2 teaspoon salt, apricots, raisins, bell pepper, onion, egg white, parsley, oregano, and pepper. Mix well.

Line a baking sheet with foil. Place peppers, cut-side up, on baking sheet; stuff with barley-spinach mixture. Sprinkle with cheese. Place on middle rack in oven for about 20 minutes. Remove and allow to cool 10 minutes before serving.

While peppers are cooking, heat vinegar in a small saucepan until boiling; reduce heat to medium-high and cook for about 5 minutes, until thickened. Remove from heat and cool slightly. Pour vinegar over peppers before serving.