Trim any excess fat from the steaks and cut into 1-inch cubes.

Place the cubed steak in a large nonreactive bowl.

Combine white onion, garlic cloves, lime juice, kosher salt, freshly ground black pepper, and saffron (steeped in boiling water) or cumin in a food processor.

Process until the mixture is smooth.

Pour the mixture over the meat and toss to coat.

Cover the bowl and marinate for 30 minutes at room temperature, or up to 12 hours in the refrigerator.

When ready to cook, heat the grill to medium heat (350 degrees F) and oil the grates well.

Thread the marinated meat onto skewers, leaving a small space between each piece.

In a small bowl, drizzle the Roma tomatoes with olive oil and season with salt and pepper.

Toss to coat the tomatoes thoroughly.

Place the meat skewers and tomatoes on the grill.

Cook the meat, turning once, until charred and medium-rare, approximately 7 to 10 minutes.

Cook the tomatoes, turning rarely, until blistered and soft, approximately 10 minutes.

Remove the meat from the skewers.

Assemble sandwiches with the grilled meat, tomatoes, lavash bread, yogurt, and cilantro.