- 8 ounces button mushrooms
- 1 medium yellow onion, peeled
- 1 large green or red bell pepper
- 1 1/2 pounds beef sirloin, fat trimmed by the butcher or an adult
- 1 tablespoon Baby Bam 
- 1/4 cup Worcestershire sauce
- 1/4 cup soy sauce
- 2 tablespoons balsamic vinegar
- 2 tablespoons vegetable oil
- 1 tablespoon chopped garlic
- Wood or metal skewers
- Place the mushrooms in a large bowl of water and gently turn to remove any grit or dirt. Dry on a clean kitchen towel and set aside.
- Cut the onion in half. Cut each half into quarters, keeping the pieces together as much as possible. Remove the upper fourth of the bell pepper. Remove the stem end, inside ribs, and seeds. Cut the pepper into quarters crosswise, then into 1-inch pieces.
- Cut the meat into 1-inch pieces and place in a large glass bowl. Add the Baby Bam and toss to coat. Add the Worcestershire sauce, soy sauce, balsamic vinegar, vegetable oil, and garlic, and stir to combine. Cover tightly with plastic wrap and refrigerate for at least 2 hours and up to 4 hours.
- Preheat the oven to 450 degrees F and place the oven rack in the top position. Line the baking sheet with aluminum foil.
- Remove the meat from the refrigerator. Thread 1 meat cube onto a skewer, followed by a mushroom, bell pepper, and onion. Continue threading alternating ingredients onto the skewer until the skewer is full. Place the filled skewers on the baking sheet and bake for 10 minutes for medium.
- Remove from the oven. With an oven mitt or tongs, hold one end of the skewer. In the other hand, with a fork, push the meat and vegetables from the skewer onto a plate. Repeat with the remaining skewers, and serve hot.