Peel the cucumber, cut in half and scrape out the seeds with a spoon. Cut the cucumber into thick slices.
Dice the bacon, peel and halve the onions and cut into thin slices.
Melt the margarine in a saucepan, leave out the bacon in it and then sweat the onions until translucent. Put the cucumber pieces with the sugar in the saucepan, stir and sweat everything for about 5 minutes over no heat, do not forget to stir. Add the sliced tomatoes and the ketchup. Season with 1 teaspoon salt and pepper. Pour up the water. Put the lid on and stew for 15 minutes. If the cucumbers are still too firm, continue to simmer for a few minutes, possibly adding a little water. Finally, bind the braised stock with cornstarch and then season to taste. Add the chopped parsley to the vegetables.
Pan-fried meat or bratwurst and boiled potatoes go well with the stewed cucumbers.