1) Preheat the oven to 180C/Gas 4. In a large mixing bowl, toss the mushrooms in the olive oil and season with salt and pepper, to taste. Lay the mushroom caps out on a rimmed baking tray, stem side up. Bake in the oven for 10 minutes, then remove from the oven.
2) Meanwhile, stir the crab, cream cheese, 1/2 the spring onion and some salt and pepper together in a mixing bowl. Preheat the grilling element.
3) Divide the stuffing among the baked mushroom caps without filling them too tightly. Top each stuffed mushroom with some spring onion, chives and grated Parmesan and grill for 2 to 3 minutes until the cheese is bubbly and the stuffing is heated through.