Preheat oven to 375 degrees. Lightly coat a baking sheet or baking pan with cooking spray.
Halve the peppers longways, then remove the cores and seeds. Place on the baking sheet
Chop the portobello mushroom, red onion, artichoke hearts, avocado and parsley. Combine in a bowl.
Add in the cooked barley and crumbled feta. Drizzle the olive oil in, and seasons with salt and pepper. Mix to combine well.
Spoon the mixture into the pepper halves. Bake for 15 minutes, or until the peppers seem tender.