01 - Whisk together olive oil, soy sauce, lemon juice, garlic, smoked paprika, cumin, pepper, and salt in a bowl. Add beef cubes and toss to coat thoroughly. Cover and refrigerate for at least 1 hour, up to 8 hours for maximum flavor and tenderness.
02 - Preheat grill or grill pan to medium-high heat, approximately 400°F.
03 - Thread beef cubes, bell pepper pieces, and onion wedges alternately onto skewers, leaving a small space between each piece to ensure even cooking.
04 - Place skewers on the preheated grill and cook for 10 to 15 minutes, turning every 3 to 4 minutes, until beef is browned and reaches desired doneness and vegetables are tender-crisp.
05 - Remove skewers from grill and let rest for 5 minutes before serving to allow juices to redistribute.