• Step 1: In a large bowl, combine the cubed beef, bell pepper pieces, and onion chunks. In a separate small bowl, whisk together the olive oil, balsamic vinegar, oregano, garlic powder, smoked paprika, and cumin. Season with salt and black pepper to taste.
• Step 2: Pour the marinade over the beef and vegetables, and toss to coat everything evenly. Cover the bowl and refrigerate for at least 30 minutes, or up to 4 hours, to allow the flavors to meld.
• Step 3: Preheat your grill to medium-high heat. Thread the marinated beef and vegetables onto skewers, alternating the ingredients as you go.
• Step 4: Grill the kebabs for 10-12 minutes, turning them occasionally, until the beef is cooked to your desired doneness and the vegetables are tender and lightly charred.
• Step 5: Remove the kebabs from the grill and let them rest for a few minutes. Serve hot, garnished with fresh parsley or cilantro if desired.