Use paper towels to blot off excess water from the tuna, then sprinkle with salt. Let sit for 5 minutes, then blot off excess water a second time. Cut tuna, avocadoes, and cucumbers into roughly ½-inch cubes. Thinly slice the scallions.
Pour cooking oil into a skillet and heat on medium. Add tuna and roll the tuna cubes around in the pan to evenly sear all sides.
Mix together seared tuna, avocado, cucumbers, Kenko creamy kingoma dressing, soy sauce, sesame oil, and white sesame seeds in a bowl.
Set a 2½ or 3-inch-diameter baking ring on a plate. Fill halfway with avocadoes and cucumbers, then layer tuna on top. Remove the baking ring and sprinkle with scallions. Drizzle additional Kenko creamy kingoma dressing on the plate and top with a dash of coarse-ground black pepper.