01 - In a medium 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, cover the bowl, and refrigerate for at least 1 hour (up to 8 hours for deeper flavor development).
03 - If using wooden skewers, soak them in water for 30 minutes prior to grilling to prevent scorching.
04 - Preheat grill or grill pan to medium-high heat, approximately 400°F.
05 - Thread marinated beef cubes, bell pepper pieces, and red onion wedges alternately onto the prepared skewers, leaving slight space between pieces for even cooking.
06 - Lightly brush assembled kebabs with olive oil and season generously with salt and pepper on all sides.
07 - Place kebabs on the preheated grill and cook for 10-12 minutes, turning every 3-4 minutes, until beef reaches desired doneness and vegetables show light char marks.
08 - Remove kebabs from grill and let rest for 2-3 minutes before serving hot.