Mix the vinegar, oil, grapefruit zest, sugar, salt and pepper in a bowl.
Add the carrots to the dressing, mix and leave to infuse for approx. 5 mins. Slice off the top and bottom of the grapefruit, then peel all round the fruit down to the flesh. Using a sharp knife, cut out the segments between the white membranes. Mix the fruit segments, resulting juice and 1 tbsp of sesame seeds in to the salad. Sprinkle with the rest of the sesame seeds.