1. Preheat broiler to high.
2. Hollow out top and bottom halves of hoagie rolls, leaving a 1-inch-thick shell; reserve torn bread for another use. Place hoagie rolls, cut sides up, on a baking sheet, and broil for 1 minute or until rolls are toasted.
3. Heat a large nonstick skillet over medium heat. Add oil; swirl to coat. Sprinkle chicken evenly with oregano, salt, and pepper. Add chicken to pan; cook 7 minutes, turning occasionally. Add bell pepper to pan; cook for 2 minutes or until bell pepper is tender and chicken is done. Stir in marinara sauce, and cook 30 seconds or until marinara is thoroughly heated.
4. Transfer top halves of rolls to a plate. Divide chicken mixture evenly among bottom halves of rolls; top evenly with cheese. Broil 1 minute or until cheese melts. Top with top halves of rolls.