01 - Whisk together olive oil, soy sauce, lemon juice, minced garlic, oregano, black pepper, and salt in a large bowl until fully combined.
02 - Add beef cubes to the marinade, toss thoroughly to coat, cover, and refrigerate for at least 1 hour or up to 8 hours for deeper flavor development.
03 - If using wooden skewers, submerge in water for 30 minutes to prevent scorching on the grill.
04 - Thread beef, bell peppers, and onion pieces alternately onto skewers, distributing evenly.
05 - Preheat grill to medium-high heat, approximately 400°F.
06 - Lightly brush assembled skewers with olive oil to promote even browning.
07 - Grill for 12 to 15 minutes, turning every 3 to 4 minutes, until beef reaches desired doneness and vegetables are tender with light charring.
08 - Remove from grill and rest for 5 minutes before serving to allow juices to redistribute.