Steakhouse Kebabs

Ingredients:
1 med. yellow onion
8  baby Yukon Gold potatoes
14-16 ounce rib eye steak
8 button mushrooms
⅓ cup extra virgin olive oil
⅓ cup balsamic vinegar
3 tablespoons fresh rosemary, chopped
2 garlic cloves, minced
1½ teaspoons salt
½ teaspoon fresh ground black pepper
4  skewers
Instructions :
Cut the steak into 16 equal pieces if using a thin cut and 8 equal pieces if using a thick cut. Season with ½ teaspoon salt and ½ teaspoon pepper. Place the steak and mushrooms in a large bowl. Add the olive oil, vinegar, rosemary, and garlic, and stir until the steak and mushrooms are well coated. Cover with plastic wrap and refrigerate at least 30 minutes to 2 hours.
Place the potatoes in a large saucepan and add enough water to cover by 1 inch. Bring the water to a boil and cook potatoes until just barely fork-tender, about 5-7 minutes. Drain and set aside. Then  cut the onion into 4 pieces.
Add a piece of steak, a potato, another piece of steak, and a mushroom to a skewer. Then add a onion chunk then another piece of steak, a potato, another piece of steak, and a mushroom again. Repeat with remaining skewers and ingredients.
Heat a grill to medium-high and lightly oil the grate. Add the kababs and grill about 5-6 minutes on both sides, flipping every 3 minutes.