Miso salmon skewers, cubed and seared on the griddle until the edges caramelize and the centers stay tender. The marinade does the work overnight, so they cook in just minutes.
Make the Marinade: To a saucepan, add the sake and mirin and bring to a simmer. Reduce by about one third. Add the miso and cane sugar, whisk well, and cook on medium-low for 2 to 3 minutes. Let cool completely.
Marinate: Add the salmon cubes to a non-reactive container and pour the cooled marinade over the top. Toss to coat. Cover and refrigerate at least 1 hour, up to 24.
Skewer: Thread the salmon cubes onto the skewers, leaving a little space between each.
Sear: Preheat a griddle to 425°F (220°C), or use a stainless steel pan over medium-high heat. Add the avocado oil and sear the skewers on all sides, 1 to 2 minutes per side, brushing with marinade from the dish as they cook, until caramelized and golden. Cook to your preferred doneness, from 120°F (49°C) for medium-rare to 145°F (63°C) for fully cooked.
Finish: Add the remaining marinade to a pot and boil for at least 5 minutes, stirring frequently. Brush over the cooked skewers.
Serve: Serve over white rice with lemon wedges and sliced green onion.