Trim excess fat from beef and cut into 1.5-inch cubes. Place in a mixing bowl.

In a small bowl, whisk together olive oil, minced garlic, cumin, coriander, paprika, lemon juice, salt, and pepper.

Pour marinade over beef cubes, toss to coat evenly, cover, and refrigerate for at least 30 minutes (up to 2 hours) to enhance flavor.

Heat grill or grill pan over medium-high heat until hot.

Thread beef cubes onto skewers, alternating with pieces of bell peppers and onions if using.

Place skewers on the grill and cook for 10-12 minutes, turning occasionally, until beef is browned and cooked to desired doneness.

Remove kebabs from grill, let rest for 2 minutes, then serve hot with side dishes.