How to Make It
In a bowl, toss the fennel with the onion, lemon juice, dill and 2 tablespoons of the oil; season with salt. Let stand at room temperature for 45 minutes.
Preheat the oven to 350°. Season the salmon with salt. In an ovenproof skillet, heat the remaining 1 1/2 teaspoons of oil until shimmering. Add the salmon fillets skin side down and, using a spatula, gently press the fillets to flatten. Cook over moderately high heat until the skin is crisp and the salmon is rare within, 5 minutes. Transfer the skillet to the oven and bake until the salmon is nearly cooked through, 2 minutes; transfer to plates, skin side up. Serve with the fennel slaw.