30 minutes before grilling, soak the skewers in water (if using wooden skewers).
Bring a pot of water to a boil. Add the potatoes and a generous pinch of kosher salt to the water. Boil for 3 minutes. Drain the potatoes in a colander. Set aside and let cool.
Heat the grill to 350-400 degrees.
In a large bowl place 3 tablespoons of olive oil, 1 1/2 teaspoon kosher salt and 3/4 teaspoon granulated garlic. Stir to combine.
Place the steak, onions and potatoes into the bowl and toss to coat. Be sure to toss gently so not to break the potato slices.
On a skewer, alternate the pieces of meat, potato and onions. Be sure to leave a little room between each ingredient to help them cook evenly. Place the skewers onto the grill. Grill 6-7 minutes per side. Serve hot.