1Cut the beef tenderloin into 1-inch cubes.
Clean the button mushrooms and cut the red onion into large chunks.
In a bowl, mix the olive oil, balsamic vinegar, minced garlic, salt, and pepper to create the marinade.
Add the beef cubes, mushrooms, and onion chunks to the marinade. Toss to coat evenly.
Cover the bowl and let it marinate in the refrigerator for at least 30 minutes.
Preheat the grill to medium-high heat.
Thread the beef, mushrooms, and onion chunks onto skewers, alternating between each ingredient.
Grill the skewers for about 8-10 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 skewers hot and enjoy!