For the raita:
Prepare raita by mixing all ingredients together, blending well. Cover and place in refrigerator until chilled, up to 4 hours.
For the burgers:
Heat 2 tablespoons olive oil in medium sized skillet over medium heat. Add onion and a teaspoon salt. Sauté until tender, approximately 5 to 6 minutes. Add curry powder and stir for about 1 minute; remove from heat. Cool mixture.
Place ground lamb in large bowl, add onion mixture, 1 teaspoon salt, cilantro, and freshly ground black pepper (approximately 1 tablespoon). Mix thoroughly and shape lamb into six ½-inch patties.
Grill lamb burgers over a medium-high grill (or under broiler). Cook for about 4 minutes or until grill marks appear. Flip burgers and cook until done; medium-rare will take approximately 4 minutes more.
Place burgers on hamburger buns or on naan/flat breads with optional tomato slices and a spoonful of raita.