Directions: Melt the butter in a large nonstick skilet over medium heat. Add the shallots and cook, stirring, until softened for about 3 min. Add the mushrooms and cook, stirring, until softened and lightly browned. Add the spinach and cook briefly, just until wilted and softened. Transfer to serving plates.
Rinse out the skillet, dry with paper towels and heat over high heat. When drops of water sizzle on the surface, add the soy mixture and the sugar mixture. Simmer for 1 min to dissolve the sugar, then arrange the salmon fillets in the pan and reduce the heat to medium.
Cook at a simmer (you should see the liquids bubbling rapidly around the fillets), adding more water, 2 tablespoons at a time as the mixture cooks dry. When the salmon has firmed up a bit and the underside is glazed, about 3 min, turn with tongues and cook for 2 - 3 min more.
Do not overcook -- the salmon should remain quite soft. Place the salmon fillets on top of the spinach mixture on the serving plates and serve immediately, sprinkled with cilantro.