Dry the fillets on paper towels; season with salt and pepper. Place the flour on a large plate. Place a very large skillet (or 2 medium skillets) over low heat with the oil. While the oil is heating, dredge the fillets in the flour, patting off the excess.

 

Turn the heat to medium-high and when the oil is hot, place the fillets in the skillet, skin side up, without crowding the pan. Saute the fillets on the first side until they're golden, about 5 minutes. Turn them, reduce the heat to medium, and continue cooking 3 to 4 minutes more, or until they're just cooked through. Remove the skillet from the heat, place the fillets on a warm platter.

 

Add the pecans to the same skillet. Toast the pecans over low heat, stirring, until they're very lightly browned and beginning to smell toasty, 30 to 60 seconds. Add the lemon juice and butter; let them sizzle together with the pecans, stirring once or twice. Turn off the heat and season with salt and pepper. To serve, top the fillets with the buttery-lemon pecans, sprinkle them with the chives, if using, and serve right away.