1Rinse rice and add to a pot with water. Bring to a boil, then reduce heat to low, cover, and simmer for 18 minutes. Remove from heat and let rest 5 minutes.
2While rice cooks, make the glaze: whisk white miso, melted butter, rice vinegar, honey, minced garlic, and minced ginger in a small bowl until smooth.
3Pat salmon fillets dry and season with salt and pepper on both sides.
4Heat a skillet over medium-high heat. Once hot, add salmon skin-side up and sear 4 minutes until the skin is crispy. Flip, brush generously with miso glaze, and cook 3 minutes more until just cooked through. Brush with remaining glaze.
5Divide cooked rice among four bowls. Top each with a salmon fillet.
6Arrange cucumber slices and napa cabbage on the side of each bowl. Drizzle the bowl with sesame oil.
7Garnish with sliced green onion and sesame seeds. Serve warm.