Preheat the oven to 375 degrees F. Place salmon in a parchment paper-lined baking dish. Drizzle with the melted butter and lime juice; season with salt and pepper. Bake 15 minutes, or until cooked through. While the salmon bakes, place the stock, garlic and chili flakes in a pot and bring to a simmer. Add the bok choy and cook until just wilted; season with salt and pepper. Divide the greens and stock among four shallow bowls, place the baked salmon on top and serve.