Preheat the oven to 400 degrees F.
Use a small amount of olive oil to grease a shallow baking dish that is just large enough to hold the stuffed fillets in 1 layer, and set aside.
Heat 1 tablespoon of the remaining olive oil in a medium-size skillet over medium heat. When it is hot, add the onion and garlic, and cook, stirring, just until the onion is softened, 3 to 5 minutes. Remove from the heat and stir in the parsley and pepper, and set aside.
Rinse the fillets and pat dry with paper towels. Lay the fillets out flat on a work surface, inside up. Spread the onion mixture down the center of each fillet, dividing evenly. Fold fillet over the onion mixture, and secure with a couple of toothpicks. Arrange the stuffed fillets in the prepared baking dish. Spoon the chopped olives evenly over the fillets. Arrange the lemon slices over the olives. Drizzle evenly with the remaining olive oil, then sprinkle lightly with paprika.
Cover the baking dish very tightly with aluminum foil, and bake for 20 minutes. Remove the foil, and test the fish for doneness. It should flake when lightly touched with a fork. Serve immediately, accompanied by hot couscous.
Recipe courtesy Jaafar Elmehdi. The New York Cabbie Cookbook, Running Press, 2003