01 - Whisk together olive oil, soy sauce, lemon juice, minced garlic, dried oregano, black pepper, and salt in a mixing bowl until fully incorporated.
02 - Add beef cubes to the marinade, toss thoroughly to coat all surfaces, cover the bowl, and refrigerate for at least 1 hour, up to 4 hours for optimal flavor penetration.
03 - If using wooden skewers, soak them in water for 30 minutes prior to grilling to prevent charring.
04 - Thread marinated beef, bell pepper pieces, and red onion chunks alternately onto skewers, leaving slight space between pieces for even cooking.
05 - Lightly brush assembled kebabs with olive oil and season generously with salt and fresh ground pepper.
06 - Heat grill or grill pan to medium-high temperature, approximately 400°F.
07 - Place kebabs on the preheated grill and cook for 10 to 15 minutes, rotating every 2 to 3 minutes, until beef reaches desired doneness and vegetables are tender with light char marks.
08 - Transfer kebabs to a serving platter and let rest for 5 minutes to allow juices to redistribute.