Preheat the oven to 190°C.
Place the sweet potatoes onto an oven tray, and bake for 50-60 minutes, until tender (test with a pointed knife in the side).
Remove from the oven, and when cool enough to handle, cut in half horizontally. Scoop out the flesh, leaving about 1 cm in the skin.
Mash the sweet potato with a fork, and add the corn, tuna and parsley. Stir in the eggs, and season to taste.
Place the sweet potato shells onto an oven tray lined with non-stick baking paper. Spoon the mixture into the sweet potato shells (if the shells are very soft, prop the sides with a little folded foil). Sprinkle cheese on top.
Bake for 25 minutes, until set and golden. Serve immediately, with salad or steamed green vegetables.