1. Marinate the steak into the balsamic vinaigrette, ground pepper, garlic powder, and whole seed brown mustard for 8 hours in the fridge prior to cooking.
2. After the meat is done marinating, cut the onions, bell peppers, and butternut squash into small chunks and set aside.
3. Cut flank steak into small square-inch sized chunks and set aside.
4. Assemble the steak and vegetables on the skewers as pictured below.
5. Bake the skewers at 400 degrees Fahrenheit in the oven for 45 minutes
6. Enjoy :)