Chop the mushroom stalks and finely
chop the onion.
Scoop out the flesh from the
tomatoes with a teaspoon.
Melt the margarine in a pan and fry
the mushroom stalks and onion over moderate heat for about 3
minutes, or until the onion is soft but not colored.
Remove from the heat and stir in
the tomato flesh, breadcrumbs, cheese, sweet corn and mint, season
with salt and pepper and add just enough egg to bind together.
Arrange the mushrooms, stalk sides
up, and the tomatoes, cut sides up, in the dish.
Spoon the cheese mixture into the
mushrooms caps and on to the tomatoes, pressing well down.