Cut red beets into strips. Clean and wash spring onions and cut into fine rings. Wash lemon hot, dry and grate half the peel. Halve the fruit and squeeze the juice from 1 half.
Rinse the maties, dab dry and cut into pieces. Mix yoghurt, beetroot, spring onions, lemon peel and maties. Season to taste with some lemon juice, salt and pepper. Cover and put in a cool place.
Remove the seeds from the melon and cut out the flesh with a ball cutter. Sort, wash, shake dry and possibly cut into smaller pieces. Arrange matie salad, melon balls and rocket on plates. Sprinkle with pepper.