The first step in making Steak Sushi is preparing the rice. Rinse 1 cup of sushi rice with water until the water runs clear. Add the rice and 1 cup of water to a pot and bring it to a boil. Once the water is boiling, reduce the heat to low, cover the pot, and simmer for 15-20 minutes, or until the water is absorbed.

In a small saucepan, combine 1 tablespoon of rice vinegar, 1 tablespoon of sugar, and 1 teaspoon of salt. Heat the mixture over low heat until the sugar and salt have dissolved. Once the rice is cooked, transfer it to a large bowl and add the vinegar mixture. Mix well and let it cool.

While the rice is cooking, prepare the steak. Heat a skillet over high heat until it's very hot. Season the thinly sliced sirloin steak with salt and pepper, and sear the steak in the skillet for about 2-3 minutes on each side until it's browned but still slightly pink in the middle. Once the steak is cooked, transfer it to a plate and let it cool.

Now, it's time to assemble the Steak Sushi. Take a sheet of nori and place it shiny side down on a sushi mat. Wet your hands with water and take a handful of rice, and spread it evenly over the nori, leaving a 1-inch border at the top edge. Sprinkle sesame seeds over the rice.

Next, arrange the avocado and cucumber slices over the rice. Place the seared steak slices on top of the avocado and cucumber, leaving a small gap between each slice. Roll the sushi tightly, using the sushi mat to shape it into a cylinder. Apply some pressure to make sure the roll is tight.

Once the sushi roll is tightly packed, remove it from the sushi mat and place it on a cutting board. Use a sharp knife to cut the roll into 1-inch slices, wiping the knife with a wet towel after each cut to keep it clean. Serve the Steak Sushi with soy sauce and wasabi on the side.