Persian Beef Kebabs

Name: Persian Beef Kebabs
Ingredients: 2 pounds sirloin steak; 1 medium white onion, roughly chopped; 5 medium garlic cloves, crushed; 1 medium lime, juiced (about 4 teaspoons); 2 tablespoons kosher salt; 2 teaspoons freshly ground black pepper; 2 pinches saffron (steeped a few minutes in 2 tablespoons boiling water) or 1 1/2 teaspoons ground cumin; 8 (12-inch) metal or wooden skewers, if wooden, soak in water for 15 minutes; 8 medium Roma tomatoes; Olive oil; Lavash bread, for serving; Plain yogurt, for serving; Cilantro leaves, for serving