1 1/4 to 1 1/2 pounds cucumber, preferably thin Asian or English variety
1/2 cup rice vinegar or 1/2 cup white vinegar diluted with 1/4 cup water
2-inch piece of fresh ginger, peeled and minced or grated
2 tablespoons sugar
1 teaspoon salt
3 tablespoons grapeseed or other neutral oil
1 pound sea scallops (cut in half through their equators if very large) or shrimp, peeled
1 medium to large onion, sliced
1/2 teaspoon ground turmeric, optional
2 tablespoons sesame seeds
With Asian or English cucumbers (or small garden cucumbers), slice thinly, preferably with a mandoline. With thick cucumbers, peel, halve lengthwise, and scoop out seeds before slicing.
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 or shrimp. Sear for about 2 minutes to a side, then remove to a plate. Turn heat to medium, add remaining oil, onions and turmeric, if you are using it. 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.