Heat oil in a medium saucepan over medium heat. Add celery, carrot and onion. Cook until vegetables start to soften, about 5 min. Add leek; cook for 2 min. Stir in barley; cook for 1 min. Add broth; bring to a boil. Reduce heat to medium-low; simmer, stirring occasionally, until barley is tender and liquid is absorbed, 25 to 30 min.
Stir in Parm cheese, sage, salt and pepper.
To add a cheesy crust to the top of this versatile side dish, spoon stuffing into an oven-safe dish. Top with 1/2 cup (125 mL) grated Parm cheese. Bake in 375˚F (190˚C) oven for 15 minutes or until cheese is melted and golden brown.