1 cup plain whole milk Greek yogurt
2 tablespoons olive oil
2 teaspoons paprika
1/2 teaspoon cumin
1/8 teaspoon cinnamon
1 teaspoon crushed red pepper flakes (reduce to 1/2 teaspoon if you don't like heat)
Zest from one lemon
2 tablespoons freshly squeezed lemon juice, from one lemon
1-3/4 teaspoons salt
1/2 teaspoon freshly ground black pepper
5 garlic cloves, minced
2-1/2 pounds boneless skinless chicken thighs (or 2 pounds boneless skinless chicken breasts), trimmed of any excess fat and cut into large bite-sized pieces
1 large red onion, cut into wedges
Vegetable oil, for greasing the grill