Prepare the marinade. In a large mixing bowl, whisk together the yogurt, lemon juice, zest, extra virgin olive oil, tomato paste, garlic, and spices.
Pat the chicken dry and season with kosher salt on both sides.
Add the chicken to the marinade, and using a pair of tongs, toss to combine, making sure all the chicken pieces are well covered in the marinade. Cover and refrigerate for 4 to 8 hours.
Heat a gas grill to medium and lightly oil the grates.
Thread the chicken pieces through skewers (you can fold larger pieces so that they would fit better through the skewers, they also look better this way and are more manageable on the grill).
Arrange the chicken skewers on the heated grill in one single layer. Cover and cook for about 15 to 20 minutes, turning every 5 to 7 minutes, until the chicken is cooked through.