01 - Whisk olive oil, soy sauce, lemon juice, minced garlic, oregano, black pepper, and salt in a large bowl to create the marinade.
02 - Add beef cubes to the marinade, toss to ensure even coating, cover, and refrigerate for at least 1 hour, or longer for enhanced flavor.
03 - Heat grill to medium-high, approximately 400°F (200°C), preparing for cooking.
04 - Alternate threading beef, bell peppers, and red onion onto skewers, spacing pieces slightly to promote even cooking.
05 - Cook kebabs on the preheated grill for 10 to 12 minutes, turning every 2 to 3 minutes until beef is cooked to preference and vegetables are tender with slight charring.
06 - Remove kebabs from grill, allow to rest for 5 minutes, then serve hot.