If using Bamboo Skewers start them soaking in water so they don't burn on the grill.
Combine cilantro, vinegar, sour cream, garlic, chile powder, cumin and 1/4 teaspoon salt in a small bowl. Set aside.
Preheat grill to high.
Toss steak, peppers and onion pieces with oil and remaining salt in a bowl. Thread steak, peppers and onions onto eight skewers. **I thread all my meats and veggies seperate as we like our steak medium rare but prefer our peppers and onions to be a little more charred. I also "double" thread the veggies (using 2 skewers, about 1/2" apart) so the veggies are easier to turn on the grill and don't just "spin" on the skewer. It takes some time but is worth it. Grill all to desired doneness.