Preheat the oven to 350 degrees F.
In a large bowl, gently mix together the ground beef, Worcestershire, garlic salt, 1 teaspoon salt and 2 teaspoons pepper. Transfer the burger mixture to a lightly greased 9-by-13-inch baking dish, pressing it into a flat layer with your hands. Evenly scatter over the diced onions; lightly press the onions into the meat.
Bake until the burger is medium rare, 15 to 20 minutes. Let rest for 5 minutes.
Gently slide the cooked burger patty out of the baking dish and onto a cutting board or platter; leave a few tablespoons of excess burger drippings in the pan. Place the bottom buns into the baking dish. Squirt yellow mustard evenly across the buns.
Place the burger patty on the buns. Divide the pickles among the sliders. Top with a layer of slightly overlapping cheese slices. Add the bun tops, pressing down on them gently.
Brush the tops of the buns with egg. Sprinkle the chips over the buns.
Return to the oven and bake until the cheese is melted, another 15 to 20 minutes.
Slice the burgers along the lines of the buns to separate into individual sliders. Scoop out with a spatula. Serve immediately.