01 - Whisk together olive oil, soy sauce, lemon juice, garlic, oregano, black pepper, and salt in a large bowl until fully combined.
02 - Add beef cubes to the marinade, toss thoroughly to coat, cover, and refrigerate for at least 1 hour, up to 8 hours for enhanced flavor development.
03 - Heat grill to medium-high temperature, approximately 400°F.
04 - Thread beef cubes, bell pepper pieces, and onion pieces alternately onto skewers, distributing ingredients evenly.
05 - Grill kebabs for 12 to 15 minutes, rotating every 3 to 4 minutes, until beef reaches desired doneness and vegetables are tender with light charring.
06 - Remove from grill and let rest for 5 minutes before serving hot.