Preheat a grill to a high heat. Pour 3 cups of water into a large saucepan, add the lentils and bring to the boil. Reduce the heat, cover and simmer for 20 minutes, or until the lentils are tender, but still holding their shape.
Meanwhile, place the capsicum quarters, skin side up, under the preheated grill and cook for 15 minutes until the skin is blackened and blistered all over. Transfer to a plastic bag, seal and leave to cool. When cool enough to handle, remove the charred skin and dice the flesh.
Mix together the diced capsicum, celery, onion, tomatoes, garlic, parsley, lemon juice and oil.
Drain the lentils, toss with the rest of the salad ingredients and season to taste. Serve warm, heaped on a bed of salad leaves, garnished with lemon slices.
• Always rinse lentils lightly in a sieve before cooking and pick through with your fingers to be sure there are no stray little stones present. * • Never add salt to pulses during cooking as it toughens them. Season later, once they are cooked and tender.