Cook the lentils in boiling water for about 25 minutes. Wash the quinoa and cook in boiling salted water for about 15 minutes. Drain the lentils and quinoa. In a bowl mix with 1 tbsp. oil. Leave to cool.
In the meantime, mix vinegar and sugar. Fold in the remaining oil in a thin stream. Season to taste with salt and pepper. Peel and finely chop the onion. Peel and grate carrots. Wash tomatoes, grate dry, cut in half, remove stalks.
Cut the tomatoes into fine cubes. Wash the coriander, shake dry and chop finely, except for a few leaves for garnishing. Cut avocado in half lengthwise along the core, unscrew halves and remove core.
Remove the flesh from the skin and cut into cubes. Sprinkle with lemon juice.
Mix lentil quinoa mixture with avocado, onion, carrots, tomatoes, vinaigrette and chopped coriander. Season to taste with salt and pepper. Divide the salad into glasses and garnish with the remaining coriander.