In a large bowl, mix together all of the marinade ingredients. Remove 1/4 cup and set aside to use for the vegetables later.
Add beef to remaining marinade and mix to coat as evenly as you can. Cover and marinate 4-6 hours in the refrigerator.
Add potatoes to a large microwave safe bowl. Add 2 tablespoons water and mircrowave, covered, 4-5 minutes or just until fork tender; drain. Place the potatoes, peppers, onions, 2 tablespoons of reserved marinade, 2 tablespoons olive oil, 1/2 teaspoon salt, 1/4 pepper. Toss until evenly coated and refrigerate until ready to use.
When ready to cook, thread beef and veggies onto skewers* (alternate beef, potatoes, peppers, and onions for a good variety on each skewer and to make them pretty!
Grease and preheat grill to medium-high heat. Grill skewers until lightly charred all over, approximately 2-3 minutes per side, basting with remaining marinade halfway through cooking.
Let rest 5 minutes before serving.
Notes
*If using wooden skewers, soak for at least 30 minutes in water before grilling threading and grilling.