Allow the tuna steak to come to room temperature by letting it stand for at least 20 minutes.
Pat the tuna dry. Sprinkle liberally with kosher salt and fresh ground black pepper on both sides.
Heat the oil in a medium skillet over medium high heat. Add the steak and cook 1 to 2 minutes per side, until lightly browned on the outside but still rare on the inside. The tuna will continue cooking while sitting.
For a medium-rare tuna steak, the internal temperature should be 130°F when measured with a food thermometer at the thickest point.
Cool for 2 minutes. Then slice the tuna against the grain into ½-inch slices and serve immediately.
Cut the ginger as thinly as you can to make wafer-thin slices or finely shred. Put in a bowl with the 4 tablespoons vinegar and 1 tablespoon water. Massage briefly to soften. Set aside.
Put the rice in a medium saucepan and add 2 ½ cups of water. Bring to a boil, cover, and simmer on low heat for 15 minutes. Sprinkle in the edamame, but don’t stir them in. Cover and cook for 7 minutes more. The rice should be tender and have absorbed all the water.
Skim the edamame off of the top of the rice, and set aside.
Add 1 tablespoon of vinegar and ½ - 1 tablespoon tamari into the rice, and stir well. Spoon onto a plate and spread out to cool quickly. Once cool, spoon into four bowls.
Top each bowl with the avocado, carrot, edamame, tomatoes and cucumber.
Spoon the ginger from the vinegar and scatter on top of the bowls. Add the remaining tamari and sesame oil to the vinegar. Spoon over the sushi bowlsl and top with sesame seeds.