Combine barley and water in a medium saucepan with a pinch of sale. Bring to a boil. Cover, reduce heat, and simmer 50-60 minutes until liquid is absorbed. Cool.
Preheat oven to 400 deg F 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 three minutes. Remove from heat; cool.
In a large bowl, combine spinach mixture with cooked barley, remaining 1/2 teaspoon salt, apricots, raisins, chopped bell pepper, onion, egg white, parsley, oregano, cheese, and pepper. Mix well.
Line a baking sheet with foil. Place peppers, cut side up on baking sheet. Stuff with barley/spinach mixture. Place in middle rack in oven for about 20 minutes. Remove and allow to cool for 10 minutes before serving.
While peppers are cooking, heat vinegar in a 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.