Cut the sirloin into 1½” cubes. Place in large bowl, season with salt and pepper. Pour in ½ cup of dressing or marinade of your choice. Cover and refrigerate a couple of hours or up to overnight.
Slice the vegetables as shown in the photos. Add all vegetables except for the mushrooms into a large bowl. Season with salt and pepper. Pour in ½ cup of dressing or marinade of your choice. Toss well. Add the mushrooms on top, but do not toss. Cover and refrigerate if marinating overnight. Otherwise, cover and set on counter until ready to cook.
While the ingredients are marinating, soak the bamboo skewers in water. When ready to skewer, alternate the steak with the vegetables on the stick.
Preheat your grill, high heat on one side and low heat on the other side. Grill the skewers on high heat, covered for 5 minutes. Then flip the kabobs, cover and grill another 5 minutes. Move the kabobs to the low heat, covered, to finish cooking, about another 2 minutes or so, depending on your desired level of doneness.