Whisk all of the marinade ingredients together in a large bowl or large freezer bag (whatever dish you are going to use to marinate your steak. Remove 1/3 cup (to use later for vegetables and basting).
Add steak to remaining marinade and turn to coat. Cover and marinate 2-6 hours in the refrigerator.
Add potatoes to a large microwave safe bowl with a tight-fitting lid. Add 3-4 tablespoons water. Microwave, covered, 4-5 minutes or just until fork tender; drain. Add peppers, onions, 3 tablespoons of Reserved Marinade, 2 tablespoons olive oil, 1/2 teaspoon salt, 1/4 pepper. Toss until evenly coated. Refrigerate. Soak wooden skewers if using at this time (they require at least 30 minutes, but I recommend soaking them when you marinate the beef). When ready to cook, thread steak and veggies onto skewers in desired order. When threading red onions, keep 2-3 slices together so they don’t burn.