Preparation

• Mix the olives, 1/3 cup of the oil, the lemon zest, lemon juice, garlic, and chile flakes in a small bowl with a fork; the vinaigrette doesn’t need to emulsify. Season with salt to taste.
• Pull out any bones in the fish with needlenose pliers or tweezers. Season both sides of the fish with salt and dredge very lightly in the flour. Heat 2 Tbs. oil in a large nonstick skillet over medium heat. When hot, add two of the fillets, skin side up; cook until light golden brown, 4 to 5 min. With a thin slotted metal spatula, turn the fish and cook until the second side is lightly browned and the fish is cooked through, about 3 min. Transfer the fillets, skin side down, to a plate, cover to keep warm. Repeat with the remaining fillets.
• Stir the vinaigrette, toss enough of it with the arugula to coat lightly (1 to 2 Tbs.), and portion it among four plates. Lay the fish on top, spoon the remaining vinaigrette over the fillets, and serve with a wedge of lemon.