Mix together the ingredients for the crust and add some salt and pepper. Rub the fish fillets in the oil and then press them into the crust mixture to coat.
Transfer the fish to a nonstick baking sheet and carefully tip over the remaining crust. Cook in a preheated oven, 220°C (425°F), Gas Mark 7, for 15 minutes until the fish is flaky and the crust is golden and crunchy.
Put the hot lentils in a bowl and stir in the remaining ingredients. Serve immediately with the fish fillets and lemon halves.