01 - In a large bowl, whisk together olive oil, soy sauce, lemon juice, minced garlic, dried oregano, black pepper, and salt until well combined.
02 - Add beef cubes to the marinade, toss thoroughly to coat all pieces. Cover the bowl and refrigerate for at least 1 hour, up to 8 hours for deeper flavor penetration.
03 - If using wooden skewers, soak them in water for 30 minutes prior to grilling to prevent burning during cooking.
04 - Thread marinated beef cubes, bell pepper pieces, and onion pieces alternately onto skewers, leaving a small space between each piece for even cooking.
05 - Preheat grill to medium-high heat, approximately 400°F.
06 - Lightly brush assembled kebabs with olive oil to prevent sticking and promote even browning.
07 - Place skewers on the preheated grill and cook for 12 to 15 minutes, turning every 3 to 4 minutes, until beef reaches desired doneness and vegetables are tender with light char marks.
08 - Remove kebabs from grill and let rest for 5 minutes before serving to allow juices to redistribute throughout the meat.