1. Heat oven to 425 degrees F. Place bell peppers on metal baking sheet; spray with nonstick cooking spray. Set aside.
2. Press 1 tsp. Sweet paprika evenly onto all surfaces of beef roast. Place roast on rack in shallow roasting pan. Do not add water or cover. Roast in oven 30-40 minutes for medium-rare doneness. Roast bell peppers in oven with meet about 30 minutes or until tender. Set peppers aside to cool.
3. Remove roast with cooked to desired temperature using instant-read thermometer. When done, transfer roast to carving board; tent with foil. Let stand 15 minutes.
4. Meanwhile, cook barley according to package directions. Set aside to cool slightly.
5. Cut beef into 1/2 inch pieces; season with salt and pepper. Whisk lime juice, oil, and 1/2 tsp. Paprika in small bowl until blended. Toss with beef, barley, toasted peppers, mangoes, green onions, and cilantro in large bowl. Serve in Boston lettuce leaves.