Thaw the shrimp in cold water. Cut the leeks in half lengthwise and each half again. Then cut 5-centimeter strips from it. Halve the large shiitake, leaving the small ones whole. Grate the ginger. Pour some olive oil in a pan and add the ginger, leeks and shiitake. Put the lid on the pan and simmer gently for about 3 minutes. Stir occasionally. Season with salt and pepper. When the vegetables are done, push them aside and add the shrimp. Fry them for 1 minute on each side or until lightly pink. Pour the soy sauce over the shrimp and season only with pepper. Arrange the vegetables on the plates and top with the shrimp. Top with sesame seeds.