Preheat the oven to 200 degrees C. Wipe the mushrooms with a damp tea towel. Remove the stalks and finely chop them. Mix 1 1/2 tablespoons of the breadcrumbs with the grated parmesan in a small bowl.
Heat the vegetable oil in a large frying pan. Add the sausage meat and cook over a moderate heat for 5 minutes, breaking it up with a spatula, until it is beginning to brown.
Stir in the onion, garlic, capsicum and mushroom stalks and cook gently for 5 minutes until soft. Stir in the remaining breadcrumbs and season with pepper. Remove from the heat.
Mound the stuffing into the mushroom caps and arrange, stuffing side up, in a large shallow baking dish. Sprinkle with the crumb mixture and drizzle with the olive oil. Bake for 8–10 minutes, or until heated through and golden.
Don't worry if you can't buy sausage meat – you can use regular sausages and just slip off the casings.