Cut off and discard the crusts from the bread; tear the bread up into pieces, put in a large bowl and pour the milk over it; set aside.
Peel and mince the garlic; toss into a frying pan with some oil; sauté for a few minutes (don't let brown), add the mushrooms, fry for a few more minutes, then add the chopped tomato, cover, and let cook for 10 minutes.
Start heating oven to 200 C / 400 F / Gas Mark 6.
Meanwhile, beat the eggs, stir into the milk and bread mixture along with the cheese.
Let the mushroom mixture cool a bit, then season as desired with salt, pepper and oregano. Then stir ⅔ of it into the egg, milk and bread mixture.
Transfer into the ovenproof dish; then spoon the remaining mushroom mixture on.
Pop into the oven, bake for 25 minutes or until it is all heated through and bubbling.