Pre-heat the oven to 300°F.
Trim the skin from the edges of the fish. Place the fish between two pieces of parchment paper and pound gently to 1/4-inch thickness.
Place the breadcrumbs in a dish. Combine the lemon and orange zests on a board. Chop with the parsley, garlic and anchovy (if using) to form a gremolata. Add to the breadcrumbs and work through with your fingers. Season the fish with salt and pepper, then gently press the fish into the breadcrumbs to coat thoroughly. In a large skillet, heat a layer of EVOO over medium-high heat.
Arrange the orange slices, arugula and onion on a platter. Top with the oregano and season liberally with salt and pepper. Dress with the lemon juice and a liberal drizzle of EVOO.
Add the fish to the hot skillet and cook in batches for 1-2 minutes on each side. Transfer to a rack-lined baking sheet and keep warm in the oven as you continue. Serve the fish with the lemon wedges and citrus salad .