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