Season salmon cubes to taste with kosher salt. Set aside.
Add soy sauce, sake, mirin, white miso, garlic, sugar, and water to a bowl and whisk until ingredients are well incorporated. Set aside.
Slice cabbage into wedges. This will ensure and encourage char on each side of cabbage. Add wedges to an oiled and scorching hot cast iron. Leave on its side for 5 to 6 minutes or until charred to desired preference. Flip to the other side and repeat. Season charred side generously with kosher salt. Once fully cooked cut cabbage into bite-sized pieces using kitchen scissors. Discard the core and remove cabbage from cast iron and cover to keep warm.
Wipe cast iron to remove bits of cabbage, then place back on the stove over medium-high heat. Add enough avocado oil to coat the bottom. Cube salmon and add to oiled cast iron. Cook for 2 minutes, flip and cook for 1 minute and repeat on all sides until salmon is slightly pink in the middle.
Add miso sauce to cast iron and lower heat. Cook until sauce is reduces and thickens. Spoon atop salmon and remove from heat.
Serve immediately; serve in bowls layered with steamed rice, charred cabbage, miso glazed salmon. Garnish with toasted sesame seeds.
