In a medium bowl, mix the marinade ingredients together. Reserve 1 tablespoon of the marinade.
1/4 cup Worcestershire sauce, 1/4 cup soy sauce, 1/4 cup olive oil, 1 Tablespoon dijon mustard, 1 Tablespoon minced garlic, 1 Tablespoon brown sugar, 2 Tablespoons lemon juice, 1 teaspoon dried basil, 1 teaspoon dried parsley, 1 teaspoon black pepper
Place the cubed meat into a large plastic zip-tight bag and pour all but the reserved marinade over it, then seal and squish to coat well. Place in the refrigerator for 1-6 hours to marinate. This is also a good time to place wooden skewers in water to soak.
1 1/2 pounds sirloin steak or sirloin tips
Meanwhile, boil the potatoes in a large pot of salted water until just tender enough to pierce with a fork, about 6-8 minutes. Drain well, then toss with 2 tablespoons of olive oil, rosemary, and mustard. Set aside.
1 pound baby Yukon gold potatoes, 2 Tablespoons dijon or whole-grain mustard, 1 Tablespoon dried rosemary, 2 Tablespoons olive oil
Preheat grill to high heat while preparing the kabobs. Chop all vegetables into chunks that are roughly the same size as the cubed steak, keeping 3 layers of onion together in each chunk. Drizzle vegetables with the reserved marinade.
8 ounces crimini mushrooms, 1 red onion, 2 green bell peppers
Thread alternating pieces of meat, vegetables, and potatoes until the skewers are filled, aiming for 4-5 pieces of steak on each skewer.
Place kabobs on the grill directly over the heat and reduce heat to medium-high. Grill for 8-10 minutes, flipping every 2-3 minutes, until the meat is cooked medium-rare to medium and the vegetables start to char just around the edges.
Remove from the grill and rest for 5 minutes before serving.