Start by cutting the chicken into 1.5 inch cubes for skewering.
Peel and thinly slice or grate the onions.
In a mortar and pestle, grind the saffron until it forms a powder, then bloom it by adding 2 tablespoons of hot water to it and allowing it to sit for 5 minutes.
Mix together the yogurt, onions, saffron, salt, pepper and lemon juice until well combined.
Marinate the chicken in the yogurt mixture, preferably in an air tight container overnight for optimal flavour.
Take the chicken out of the fridge 30 minutes before grilling.
Skewer the chicken if you are grilling, preferably on metal skewers. You can also use wood skewers, but make sure to soak them in water for 1 hour before using.
Grill the chicken on an outdoor grill, a stove top skillet or grill pan on medium heat for about 5-6 mins on each side. Ensure chicken is white and cooked through on the inside, and golden on the outside.
You can also bake in the oven for 20-25 mins at 400F, turning half way.
Serve with bread, and if you like some grilled onions, grilled tomatoes, sumac onions and salad on the side.