Arrange the haddock fillets in a lightly greased casserole. Mash the butter or margarine with the spring onions and salt and pepper to taste. Grate the rind from the grapefruit and beat into the butter or margarine.

Spread this over the haddock fillets. Cover with the mushrooms.

Squeeze the juice from one grapefruit and peel and segment the other. Pour the grapefruit juice over the mushrooms and place the grapefruit segments on top.

Cover and cook in the oven for about 30 minutes, or until the fish is cooked.

To peel the grapefruit, remove the skin in sections, cutting deeply enough to remove the pith. Using the tip of the knife, ease out the skinless segments.