In a small bowl, whisk together soy sauce, honey, garlic, sake, miso paste and ginger until well combined.
Add salmon to a small, rimmed casserole dish, and pour the marinade over the top. Refrigerate for at least 30 minutes or overnight.
Make the rice:
In a medium saucepan set over medium-high heat, whisk together water, coconut milk and salt to combine. Bring mixture to a boil, stir in rice, and lower the heat to a simmer. Cover and simmer for 15 to 20 minutes, or until most of the liquid is absorbed. Remove from heat and allow to sit, covered, for another five minutes. Fluff the rice with a fork and stir in the scallions.
Cook the salmon:
Preheat oven to 400 degrees F, and prepare a baking sheet with parchment paper.
Preheat a large cast-iron or ovenproof skillet over medium-high heat and drizzle with vegetable oil. Sear the top of the salmon for about 1 minute until a golden crust forms and the salmon easily releases from the pan. Flip the salmon fillets and immediately transfer the skillet to the preheated oven. Bake for 15 to 20 minutes. Make sure to reserve any leftover marinade.
Pour remaining reserved marinade into a small saucepan over medium-high heat and simmer for about 5 minutes until reduced.
Serve salmon over coconut-scallion rice, drizzle with reduced sauce, and garnish with sliced scallions.