In a medium bowl, whisk together olive oil, soy sauce, balsamic vinegar, minced garlic, salt, and pepper until well combined.

Cut the sirloin steak into uniform cubes, about 1.5 inches in size. Add these to the marinade, tossing gently to coat. Cover and marinate for at least 30 minutes.

Soak wooden skewers in water for 30 minutes. Preheat your grill to medium-high heat (400–450°F).

Thread the cubed steak onto the skewers, alternating with bell pepper, red onion, zucchini, and cherry tomatoes.

Grill kabobs for 10-12 minutes, turning occasionally, until nicely charred and cooked to desired doneness.

Remove kabobs from grill, let rest for 5 minutes, then serve with your choice of sides.