Combine the ingredients for the marinade in a small bowl. Whisk until smooth. Pour the marinade over the cubed sirloin. Stir to combine. Cover and refrigerate for 1 to 24 hours.
1/2 cup olive oil, 1/3 cup soy sauce, 1 tablespoon brown sugar, 1 tablespoon lemon juice, 2 tablespoons Worcestershire sauce, 2 cloves garlic, 1/4 teaspoon black pepper, 2 pounds top sirloin
Preheat your grill to medium heat. See note about cooking indoors.
After the meat has marinated, put together the skewers by adding meat, then the vegetables, then another piece of meat to the skewer. Repeat until the skewer is full. You can see in the photos I did about five pieces of meat, and four sets of vegetables for each skewer to make ten skewers.
1 large red onion, 2 red bell pepper, 2 yellow squash
Place the skewers on the grill and grill for six minutes on each side. It works best to use metal tongs to flip the skewers. Serve warm, testing the metal skewers before handing them off to kids to ensure they aren't too hot to touch.