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 with plastic wrap and refrigerate for at least 2 hours, or up to 8 hours for deeper flavor penetration.
03 - Set your gas or charcoal grill to medium-high heat and allow it to preheat fully, approximately 10 to 15 minutes. Clean and oil the grates to prevent sticking.
04 - Thread the marinated steak cubes alternately with red bell pepper, yellow bell pepper, red onion wedges, and whole mushrooms onto the prepared skewers, 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.