For the Marinade:

• 1/4 cup balsamic vinegar
• ¼ cup soy sauce
• 3 tablespoons Worcestershire sauce 
• 2 tablespoons olive oil
• 2 tablespoons fresh Rosemary finely chopped
• 3 cloves garlic finely minced
• 2 teaspoons Dijon mustard
• 1 teaspoon black pepper
• ¼ teaspoon onion powder

For the Kabobs:

• 1 pound beef sirloin cut into 1 inch pieces
• 1 8 oz package mushrooms, cleaned and cut in half
• 1 package multi-colored peppers cleaned and cut into 1 inch pieces
• 1 large red onion cleaned and cut into 1 inch pieces
• 1-2 tablespoons olive oil
• salt and pepper to taste