Thinly slice the cucumbers, preferably with a mandoline.

Mix vinegar, ginger, sugar and salt and toss with cucumbers. Let stand for 30 to 60 minutes. (Refrigerate if marinating for more than an hour in warm weather.)

Just before serving, drain excess liquid. Put 2 tablespoons oil in a skillet, preferably nonstick, over medium-high heat. Wait a minute, then add scallops. Sear for about 2 minutes to a side, then remove to a plate. Turn heat to medium, add remaining oil, onions and turmeric. Cook until onion softens, about 5 minutes.

Meanwhile, toast sesame seeds in a dry skillet over medium heat until browned and fragrant, 3 to 5 minutes. Stir onions into cucumbers, top with scallops or shrimp, garnish with sesame seeds and serve.