01 - In a bowl, whisk together olive oil, soy sauce, lemon juice, garlic, smoked paprika, cumin, pepper, and salt. Add beef cubes and toss to coat thoroughly.
02 - Cover the bowl and refrigerate for at least 1 hour, up to 8 hours for optimal flavor and tenderness.
03 - Preheat grill or grill pan to medium-high heat.
04 - Thread beef, bell peppers, and onion alternately onto skewers, leaving a little space between each piece for even cooking.
05 - Grill kebabs for 10 to 15 minutes, turning every 3 to 4 minutes, until beef is browned and cooked to desired doneness and vegetables are tender-crisp.
06 - Remove from grill and let rest for 5 minutes before serving.