Marinate the chicken cubes in a glass or ceramic bowl or pan with the olive oil, lemon juice, onion, cinnamon, cardamom, thyme, salt, pepper, cumin, if using, Baharat, and paprika for 6 hours, covered, in the refrigerator, turning the cubes occasionally.
Preheat a gas grill for 15 minutes on high or prepare a hot charcoal fire. Skewer the chicken cubes so they touch each other but do not press against each other. If possible, use a skewer rack so the chicken grills without touching the grilling grate. Grill until golden brown, 20 to 30 minutes, turning frequently. Serve hot.
Grind the peppercorns and allspice together and blend with the cinnamon and nutmeg. Store in a jar in your spice rack, away from sunlight. It will lose pungency as time goes by, but, properly stored, it will be good for many months.
Yield: 1/2 cup