Preheat oven to 200°C. Blanch mushroom caps in a pan of boiling water for 2 minutes. Drain on paper towels.
Heat oil in a large frying pan over medium heat. Add onion and garlic; sauté for 5 minutes. Add carrot and capsicum; cook for 4 minutes. Add the stock and oregano; cook for 4 minutes or until the vegetables are very soft. Remove from heat; stir in parmesan and parsley.
Spoon mixture into the mushroom caps and place on a baking tray. Bake for 10 minutes or until piping hot.
DID YOU KNOW
...that cooking mushrooms breaks down their fibrous cell walls, which makes some of their nutrients more available to the body?