In a bowl, whisk together the vinaigrette, barbecue sauce, and mustard. Set aside half of the mixture in another bowl to use later for basting.

Add the beef to the remaining sauce mixture and toss to coat.

Thread meat on skewers alternating with the tomatoes (I used 10 skewers).

Grill over medium heat 6-9 minutes until beef reaches desired doneness, turning occasionally and basting with reserved sauce during the last couple minutes of cooking.