Cut the grapefruit across the centre and loosen the segments of fruit in each half. Tip the grapefruit segments and juice out into a basin. With the fingers pull away the membrane and pith from the centre of the grapefruit so that the shells may be used for serving. With a pair of scissors snip a zig-zag round the rim of each shell and then set aside.
Remove the pips from the segments of grapefruit and strain off the juice. Add the cottage cheese and the dressing to the grapefruit and using a fork, toss to mix. Taste and add more dressing if liked. Finally mix in the chopped parsley and spoon the mixture back into the prepared shells for serving.