Heat oven to 275ºF. Season salmon with salt and pepper then add to a 3-quart, 13-inch x 9-inch baking dish. Arrange fennel and garlic around the filet and add enough extra virgin olive oil to cover.
Cover the pan dish with aluminum foil and bake until the salmon is completely cooked through, about 1 hour.
For the lemon herb salad:
In a medium mixing bowl toss together the arugula, parsley, lemon zest, pickled onions and watermelon radish with 1 tablespoon of the poaching oil and top with the fennel fronds.
For serving:
Divide salmon and fennel among plates and top with the lemon herb salad.