01 - Combine olive oil, soy sauce, lemon juice, minced garlic, oregano, black pepper, and salt in a large bowl. Whisk until well blended.
02 - Add beef cubes to the marinade. Toss to coat evenly, cover, and refrigerate for at least 1 hour, up to 8 hours for enhanced flavor.
03 - Heat the grill to medium-high, approximately 400°F.
04 - Thread marinated beef, red, yellow, and green bell peppers, and red onion wedges alternately onto skewers, dividing ingredients evenly.
05 - Place skewers on the grill and cook for 10 to 12 minutes, turning every 3 to 4 minutes, until beef is charred outside and cooked to preferred doneness.
06 - Remove kebabs from grill and let rest for 5 minutes before serving.