Place a large skillet over medium-high heat. Drizzle the salmon with 3 tablespoons of olive oil and season with salt and pepper. Cook the salmon for 5 to 7 minutes per side, until the fish is cooked through and flakes easily.
Meanwhile, heat the remaining 2 tablespoons of olive oil in a large skillet over medium-high heat. Add the onion, kale, and garlic, season with salt and pepper, and cook for 6 to 7 minutes, stirring occasionally, until the kale is wilted. Stir in the juice of 1 lemon and the cannellini beans and cook for 2 to 3 minutes, just until the beans are warmed through. Season with salt and pepper, to taste.
Stir together the yogurt, mustard, honey, and remaining lemon juice in a small bowl.
To serve, divide the kale mixture between 6 plates. Place a salmon fillet on each plate and spoon the mustard sauce over the fish. Sprinkle the chives over the top and serve.