Halve the cucumber lengthways, scrape out the seeds and cut the pulp into small, fine cubes. Add the finely chopped onion, coriander greens, sugar (or honey) to the cucumber cubes, season with salt, pepper and lime juice and let it steep for about 1.5 hours.
Maple syrup works very well as a sweetener (instead of sugar or honey), but then I would leave out the coriander or reduce the amount.
Goes well with grilled fish (e.g. salmon steaks) or poultry (e.g. corn chickens).