Not your standard stuffed mushroom. We find making the stuffing the day before and makes for easier stuffing since the starch from the rice and barley become sticky and looks great when stuffing with a serving scoop.
Rinse rice in fine strainer under cold running water; drain and set aside. Heat 1 tablespoon oil in 3 quart saucepan over medium heat. Add onion to oil; cook and stir about 10 minutes. Add barley, rice and garlic; cook and stir over medium heat 1 minute. Stir in chicken broth. Bring to a boil over medium-high heat. Reduce heat to low; simmer, covered, about 1 hour.
Clean mushrooms with a soft cloth and remove stems microwave for 3 mins to slightly cook. Set caps aside; finely chop stems. Heat remaining 1 tablespoon oil in a large skillet over medium-high heat. Add bell pepper; chopped mushroom stems, carrot and oregano; cook and stir 5 to 6 minutes. Stir the bell pepper mixture into saucepan of rice mixture. Remove from heat.
Preheat oven to 350F.
Slightly over stuff mushroom caps with rice mixture. Spray baking dish with cooking spray. Place the stuffed mushrooms in a single layer and bake, uncovered, 15 minutes at 350F. Serve hot from the oven.