Cook lentils in a large saucepan of boiling water for 20 minutes or until tender. Drain.
Meanwhile, heat a chargrill pan over high heat. Spray fennel slices with oil. Cook for 2 minutes each side or until tender.
Process the yoghurt, parsley, chives, tarragon, capers and lemon rind in a food processor until smooth. Season with pepper.
Place onion, juice, sugar and a pinch of salt in a bowl. Set aside for 5 minutes. Drain.
Combine the lentils, fennel, onion, spinach and avocado in a large bowl. Divide among plates. Top with salmon. Sprinkle with the reserved fennel fronds and extra parsley. Drizzle with the green goddess dressing.