In Peru, where this recipe originated, the avocados are stuffed with potatoes with yellow flesh. If you want the authentic look, add a couple of drops of yellow food colouring to the potato mixture. Peel 12 cooked prawns and set aside. Chop 3 cobs of corn into 4-5 cm rounds and steam or boil until tender. Steam or boil 500 g of potatoes until tender. drain and mash very smooth. Mix in tablespoons grated onions, 1/2 teaspoon chilli powder (or to taste), 3 tablespoons olive oil and salt and white pepper to taste. Cut 3 large avocados in half remove the stones and fill with the potato mixture. Put on serving plates and top each half with 2 prawns and 23 black olives. Add corn rounds to the plates. Serve warm or at room temperature.