Combine the onion quarters, lemon juice, saffron threads and olive oil, salt and pepper in the bowl of a food processor. Process until the mixture turns into a smooth paste.
Marinade chicken cubes with the paste for two hours.
Position an oven rack 8cm from the broiler and preheat the broiler. Have ready a broiler pan lined with aluminum foil.
Tightly pack the chicken pieces onto metal skewers or place them directly in the prepared pan (discarding the marinade). Broil four to six minutes, turn the chicken over and broil for another four to six minutes, or until chicken is cooked through but still moist.
Serve warm with pita bread and hummus dip. Serves four.