01 - In a large mixing bowl, whisk together the soy sauce, olive oil, balsamic vinegar, Worcestershire sauce, minced garlic, brown sugar, smoked paprika, black pepper, and dried thyme until well combined.
02 - Add the steak cubes to the marinade and toss thoroughly to coat evenly. Cover the bowl and refrigerate for at least 2 hours, or up to 8 hours for deeper flavor penetration.
03 - Preheat your gas or charcoal grill to medium-high heat, aiming for a surface temperature of around 400°F.
04 - Thread the marinated steak cubes, red and yellow bell pepper pieces, red onion wedges, and whole mushrooms onto the skewers in an alternating pattern, distributing ingredients evenly across all 8 skewers.
05 - Place the skewers on the preheated grill and cook for 10 to 15 minutes, turning every 2 to 3 minutes with tongs, until the steak reaches your desired doneness and the vegetables develop a light char.
06 - Remove the kebabs from the grill and let them rest for 5 minutes to allow the juices to redistribute before serving.