Put the mint, oregano, ham, garlic and spring onions in a bowl. Crumble in the feta cheese, season with plenty of pepper and mix together well.
Put the fish fillets skinned-side up on the work surface and press the feta mixture down the centres. Roll up loosely and secure with wooden cocktail sticks.
Scatter the courgettes into a shallow, ovenproof dish and drizzle with 1 tablespoon of the oil. Place in a preheated oven, 190°C (375°F), Gas Mark 5, for 15 minutes. Remove from the oven and add the plaice fillets to the dish. Tuck the mushrooms, tomatoes and capers around the fish and season lightly. Drizzle with the remaining oil.
Return to the oven for a further 25 minutes or until the fish is cooked through.