In a large skillet with a lid, heat butter and 2 tbsp of water. When steaming, add spinach and cover for about 5 minutes or until spinach is wilted. When done, set aside. Clean out your skillet and dry.
Place the skillet over medium heat, add olive oil. When hot, add onion, ginger, garlic, pepper,, and crushed red pepper. Cook, stirring occasionally, until softened, about 3 minutes. Add miso and cook, stirring frequently, until miso is lightly caramelized, about 5 minutes.
Add coconut milk and stock, and bring to a boil over high heat. Cook until liquid is reduced and has thickened a bit, about 5 minutes. Stir in lime juice and turmeric.
Reduce the heat to medium-low, add salmon to the sauce and cover and simmer gently until just cooked through, about 3 1/2 minutes. Lift lid and gently turn salmon over and cook another 3 minutes. Add spinach, 2 tablespoons of both cilantro and basil, lime juice, and a couple shakes of fish sauce (no more than a tsp worth). Gently stir without disturbing the salmon.
Divide rice among bowls. Add sauce and place salmon on top. Sprinkle with leftover basil, cilantro, and Serrano pepper.
