- In a bowl, combine all of the ingredients. Cover and refrigerate for 8 hours.
- Preheat the grill, setting the burners to high. Oil the grate.
- In a bowl, combine the bell peppers, zucchini and tomatoes with the oil. Season with salt and pepper. Thread the meat and vegetables onto the skewers, alternating about 4 cubes of meat and 3 pieces of each vegetable per skewer.
- Grill the skewers for 4 minutes on each side or until the meat is cooked to medium rare.
- Serve with the hummus and lemon wedges.
Sumac is a Turkish spice. These small purple dried berries can be used whole or ground. Sumac has a tangy taste reminiscent of lemon and is found in some specialty shops or Middle Eastern grocery stores.