Combine crumbs with lemon zest, pepper and salt. Coat sole in flour, shaking off excess. Coat in egg mixture, making sure it is evenly coated. Set fillets in crumbs and coat on both sides, gently pressing them in. Heat oil in large skillet set over medium, medium-high heat. Cook sole 3-5 minutes per side, depending on thickness, until nicely coloured and cooked through.