In a large bowl, whisk together soy sauce, olive oil, red wine vinegar, brown sugar, garlic, black pepper, onion powder, paprika, and salt.
Add the beef cubes to the marinade, ensuring they are well coated. Cover and refrigerate for at least 2 hours, or overnight for best flavor.
Preheat your grill to medium-high heat.
Thread the marinated beef, bell pepper, and onion onto the skewers, alternating between the beef and vegetables.
Place the skewers on the grill and cook for about 10-12 minutes, turning occasionally, until the beef is cooked to your desired doneness and the vegetables are tender.
Remove from the grill and let rest for 5 minutes before serving. Serve with rice or a fresh salad.