Rinse the sushi rice under cold water until the water runs clear. Combine the rinsed rice and water in a medium saucepan. Bring to a boil, then reduce heat to low, cover, and simmer for 18-20 minutes or until the rice is tender and water is absorbed. Remove from heat and let it sit, covered, for 10 minutes.

In a small bowl, mix the rice vinegar, sugar, and salt until dissolved. Gently fold this mixture into the cooked rice. Spread the rice on a baking sheet to cool to room temperature.

While the rice cools, heat the sesame oil in a skillet over medium-high heat. Season the salmon fillet with salt and sear for about 3-4 minutes on each side until cooked through. Remove from heat and let it rest for a few minutes before flaking it into bite-sized pieces.

In the same skillet, melt the butter over medium heat. Once melted, add the cooled rice and press it down firmly into an even layer. Cook for about 5-7 minutes until the bottom is golden and crispy. Carefully flip the rice to crisp the other side for another 5-7 minutes.

Once both sides are crispy, remove the rice from the skillet and cut it into squares or rectangles. Top each piece with flaked salmon, avocado slices, and a sprinkle of green onions and sesame seeds.

Serve with wasabi and pickled ginger on the side, if desired.