1/4 cup olive oil
1/2 medium onion, finely chopped (3/4 cup)
1 small flat fennel bulb, trimmed, cored and finely chopped (about 3/4 cup), with fronds reserved for garnish
1/2 cup orange-lemon marmalade
20 pitted whole Gaeta or kalamata (black) olives
1/4 bunch flat-leaf parsley leaves, finely chopped (1/3 cup)
15 grape or cherry tomatoes, cut in half
1 1/2 pounds (1 large piece) 1 1/2-inch-thick, skinless fish fillet, such as swordfish
Freshly ground black pepper
2 tablespoons flour
1/2 cup dry white wine, such as sauvignon blanc
1 small orange, cut into thin slices, for garnish
Heat 2 tablespoons of the oil in a large, heavy, ovenproof skillet over medium-high heat. Add the onion and stir to coat evenly. Reduce the heat to low; cook, stirring occasionally, for about 10 minutes, until the onion has softened and picked up some color.
Add the fennel and cook for about 8 minutes, stirring, or until it has softened. Turn off the heat and add the marmalade and olives; stir to mix well. Let sit for a few minutes; the skillet’s heat will melt the marmalade slightly and release some liquid from the olives to form a light sauce. Transfer the mixture to a medium bowl, then add the parsley and tomato halves; toss to combine.
Place the skillet over medium-high heat; add the remaining oil.
While the oil is heating, season the fish with salt and pepper to taste, then lightly dust with flour, shaking off any excess. Place the fillet in the skillet; sear for about 1 1/2 minutes on each side, using 2 spatulas to gently turn it over.
Spoon the sauce mixture over the fish, then transfer the skillet to the oven. Roast for 15 to 20 minutes, until the fish flakes easily with a fork. Use 2 spatulas to transfer the fish to a serving platter while you finish the sauce.
Place the skillet over high heat on the stove top; add the wine to deglaze it, using a wooden spoon or spatula to dislodge any browned bits in the skillet. Cook, stirring, for 2 to 3 minutes or just long enough for the wine to reduce by half.
Divide the fillet into equal individual portions. Spoon the sauce over the fish; garnish with the reserved fennel fronds and orange slices. Serve warm.