01 - In a large bowl, whisk 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, cover, and refrigerate for at least 1 hour or up to overnight for enhanced flavor.
03 - Heat grill to medium-high, approximately 400°F (200°C), ensuring it is clean and oiled to prevent sticking.
04 - Thread beef, bell peppers, and red onion alternately onto skewers, spacing pieces slightly to allow even heat circulation.
05 - Place skewers on the grill and cook for 10 to 12 minutes, turning every 2 to 3 minutes, until beef reaches desired doneness and vegetables are tender with slight charring.
06 - Remove skewers from grill, let rest for 5 minutes to redistribute juices, then serve immediately while hot.