Put matzoh on a foil-lined backing sheet. Heavily spread grated cheese on matzoh, not quite reaching the edges. Sprinkle on garlic, cover with a single layer of mushrooms.
Broil until the edges of the matzoh turn brown and cheese is melted.
Cut into quarters with a chef's knife, let cool for two minutes, and serve.
Ratio of ingredients is arbitrary and up to personal taste.