Cut your chicken into 1 ½ inch pieces, set aside.
In a mortar and pestle (If you don't have one of those, just grind it in a small bowl using the back of a small spoon or crush with your fingers) grind saffron until powdered.
Dissolve the crushed saffron threads in 1 tablespoon of hot water in a bowl for 15 to 20 minutes.
Add the diced onion and lemon juice to a blender and puree into a smooth paste.
Combine the marinade ingredients — saffron water, onion-lemon juice paste, yogurt, pepper, salt and mix well.
Add the marinade to the cubed chicken breast in either a zip lock bag or a bowl and allow the chicken cubes to marinate for a minimum of 12 hours but preferably up to 24 hours to overnight for the best tasting kebabs. (PRO TIP: I have marinated mine before for up to 48 hours! The longer they marinate, the more tender and juicy they will be.).