01 - In a large bowl, combine olive oil, soy sauce, lemon juice, minced garlic, oregano, black pepper, and salt; whisk thoroughly.
02 - Add beef cubes to the marinade, toss to coat evenly, cover, and refrigerate for at least 1 hour or overnight for enhanced flavor.
03 - Heat grill to medium-high, approximately 400°F (200°C).
04 - Thread beef, bell peppers, and red onion alternately onto skewers, leaving small gaps between pieces to ensure even cooking.
05 - Cook skewers on the grill for 10 to 12 minutes, turning every 2 to 3 minutes, until beef reaches desired doneness and vegetables are tender with slight char.
06 - Remove kebabs from grill, allow to rest for 5 minutes, then serve hot.