Cut the beef into 1¼-inch (3.25 cm) cubes.

In a large bowl, whisk together the garlic, onion powder, soy sauce, Worcestershire sauce, balsamic vinegar, vegetable oil, and black pepper.

Add the beef to the marinade and toss until evenly coated.

Cover and refrigerate for at least 3 hours, or up to 24 hours for maximum flavor.

Cut the bell peppers and red onion into large, even-sized squares.

Clean the mushrooms and leave them whole if they're small.

Thread the marinated beef, peppers, onions, and mushrooms onto the skewers, alternating the ingredients for colorful presentation. Leave a little space between each piece to promote even cooking.

Reserve any remaining marinade and lightly brush it over the assembled Beef Kebabs.

Drizzle the skewers lightly with olive oil.

Preheat a grill, barbecue, or heavy skillet over high heat.

Cook the kebabs for about 2 minutes on each side, turning until all four sides are nicely browned and lightly charred, about 8 minutes total.

Baste occasionally with the reserved marinade while cooking.

Transfer the kebabs to a serving platter, cover loosely with foil, and let them rest for 3 minutes.

Garnish with chopped parsley and serve with your favorite dipping sauce.