1Cut the beef sirloin into bite-sized cubes.
Clean the button mushrooms and cut the red onion into large chunks.
In a bowl, mix the soy sauce, olive oil, black pepper, garlic powder, and salt to taste.
Add the beef cubes to the marinade and let it sit for at least 30 minutes.
Preheat the grill to medium-high heat.
Thread the beef, mushrooms, and red onion chunks onto skewers, alternating between each ingredient.
Grill the skewers for about 10-12 minutes, turning occasionally, until the beef is cooked to your desired level of doneness.
Remove the skewers from the grill and let them rest for a few minutes before serving.
Serve the Beef and Mushroom Skewers hot and enjoy!