Heat toaster oven to 350° F. Drizzle 2 tablespoons of the oil over the toaster-oven baking tray and tilt to coat.
In a large bowl, combine the beef, bread crumbs, 1/2 cup of the pesto, the egg, salt, and pepper. With your hands, mix just until combined. Shape the mixture into 12 meatballs, using about 1/4 cup for each. Transfer the meatballs to tray. Bake for 15 minutes. Turn and bake until cooked through, about 10 minutes more.
Meanwhile, prepare the couscous according to the package directions.
In a small bowl, combine the remaining pesto and oil. Spoon the mixture over the cooked meatballs and turn to coat. Divide the meatballs and couscous among individual plates and sprinkle with the Parmesan (if using).