1If possible, combine the herbs with the yogurt a few hours before serving, to allow their flavors to develop. Beat the olive oil with the lemon juice. Peel and seed the cucumber and peel the avocado. Finely dice the cucumber, olives, and avocado. Combine these ingredients together with a tablespoon of the oil-and-lemon sauce. Set aside in the refrigerator.
2Just before serving, combine the remaining dressing with the yogurt sauce, and season with salt and pepper. Using a stainless steel ring or glass approximately 2 1/2 inches in diameter, shape the tartare mixture into mounds in the center of plates, and pour the raita around and over them.
Tip: If you are short of time, you can cut the vegetables into larger pieces, put them in a single large dish, and serve the raita separately.