01 - In a large bowl, whisk together olive oil, soy sauce, lemon juice, garlic, oregano, black pepper, and salt to make the marinade.
02 - Add the beef cubes to the marinade, toss to coat, cover, and refrigerate for at least 1 hour (up to 8 hours for more flavor).
03 - Preheat grill to medium-high heat (about 400°F).
04 - Thread beef, bell peppers, and onion pieces alternately onto skewers.
05 - Grill kebabs for 12–15 minutes, turning every 3–4 minutes, until beef is cooked to your desired doneness and vegetables are tender and lightly charred.
06 - Remove from grill, rest for 5 minutes, then serve hot.