Wipe the mushrooms clean with damp kitchen paper, then remove the stalks and chop them.
Heat the oil in a small saucepan, add the chopped mushroom stalks, spring onions, red pepper, courgette, olives and oats and fry gently until the oats are golden. Stir in the basil, soy sauce and lime juice.
Brush the mushroom caps with oil and place on a baking sheet. Spoon the oat mixture on to the mushrooms and season with salt and pepper. Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 15–20 minutes until the caps begin to soften, then serve.