Crush the garlic and salt together with the flat of a knife.

Put the margarine into a large bowl and place in the microwave. Heat on full power for 1 minute. Stir until melted. Add the mushrooms, garlic and pepper to taste. Toss the mushrooms to coat with the margarine mixture. Cook on full power for 5 minutes, stirring occasionally until the mushrooms are tender but not soft.

While the mushrooms are cooking, toast the bread. Using a slotted spoon, pile the cooked mushrooms on to the hot toast.

Blend the arrowroot with 1 tablespoon cold water and stir into the remaining juices. Cook for 1 minute or until thickened, stirring once during and once after cooking. Pour the sauce over the mushrooms, sprinkle with parsley and serve hot.