01 - In a large bowl, whisk together olive oil, soy sauce, lemon juice, minced garlic, dried oregano, black pepper, and salt until well combined. Add beef cubes and toss to coat thoroughly. Cover and refrigerate for at least 1 hour, up to 8 hours for deeper flavor penetration.
02 - Preheat grill to medium-high heat, approximately 400°F.
03 - In a separate bowl, toss bell pepper and onion pieces with 1 tablespoon olive oil, 1/2 teaspoon salt, and 1/2 teaspoon black pepper until evenly coated.
04 - Thread beef cubes, pepper pieces, and onion pieces alternately onto metal or pre-soaked wooden skewers, beginning and ending with a piece of beef for even cooking.
05 - Place skewers on the preheated grill and cook for 10 to 12 minutes, turning occasionally, until beef reaches desired doneness and vegetables are charred and tender. For medium-rare beef, grill approximately 10 minutes.
06 - Remove skewers from grill and let rest for 5 minutes before serving to allow juices to redistribute. Serve with rice, flatbread, or fresh green salad.