Heat oven to 400° F. In a large roasting pan, toss the fennel, lemons, garlic, 1 tablespoon of the oil, and ¼ teaspoon each salt and pepper.
Roast until the fennel begins to soften, 6 to 8 minutes.
Season the salmon with ½ teaspoon salt and ¼ teaspoon pepper and nestle in the fennel. Roast until the salmon is opaque throughout, 12 to 15 minutes.
Squeeze the garlic out of the skins into a bowl and mash to a paste. Squeeze the lemon pulp and juice into the bowl. Stir in the honey, rosemary, remaining 2 tablespoons of oil, and ¼ teaspoon salt.
Divide the greens among plates, top with the salmon and fennel, and drizzle with the dressing.