Put an Italian spin on skewers a pair a balsamic vinegar and rosemary marinade with tender pieces of beef, button mushroom, and peppers.
Combine vinegar, oil, rosemary, and 1 teaspoon salt and 2 teaspoons pepper. Reserve and refrigerate about 1/4 cup of marinade. Transfer remaining marinade to a zip-top bag and add beef and toss to coat. Refrigerate 8 hours (or up to overnight).
Heat a grill or grill pan to medium-high. Clean and lightly oil hot grill. Thread some skewers with beef, others with mushrooms, and others with peppers. Season with salt and pepper. Grill mushroom and pepper skewers for 9 to 12 minutes and beef skewers for 12 to 15 minutes, turning all skewers frequently and brushing with reserved marinade.