For the chicken skewers: Combine the lemon juice, olive oil, oregano, salt, pepper and garlic, along with 1 tablespoon of water, in a bowl.
Add the chicken pieces and toss to coat. Marinate for at least 10 minutes or up to 1 hour.
Heat a grill or grill pan over medium or preheat the broiler.
Remove the chicken from the marinade and thread the chicken pieces onto 4 skewers.
If grilling, place the chicken on the grill and cook for 5 minutes on each side or until chicken is cooked through.
For broiling, broil for 8-10 minutes or until chicken is cooked through.
While the chicken is cooking make the sauces.
For the yogurt sauce: Mix together the Greek yogurt, sour cream, cucumber and parsley. Season with salt and pepper to taste.
Refrigerate until ready for use, or for up to 1 day.
For the relish: Combine the tomato, cucumber and parsley in a bowl. Stir in the lemon juice and olive oil.
Season to taste with salt and pepper. Refrigerate until ready for use, or for up to 1 day.
Serve the chicken skewers with the yogurt sauce and cucumber relish, as well as flatbread, hummus and olives if desired.