Begin by preparing the caramelized onions. Heat the olive oil in a large skillet set over medium heat. Add the thinly sliced onions and season with a pinch of kosher salt. Lower the heat to medium-low and allow the onions to cook slowly, stirring occasionally, until they become deeply golden and jam-like in texture, about 25 minutes. Once done, set them aside to cool slightly.

Preheat your oven to 350°F. In a medium mixing bowl, stir together the melted butter, poppy seeds, minced garlic, and Worcestershire sauce until well combined.

Prepare the sliders by carefully slicing the Hawaiian rolls in half horizontally, keeping the tops and bottoms intact as a sheet. Place the bottom half of the rolls on a baking sheet. Spread a generous layer of mayonnaise across the bottom portion of the slider buns. Layer half of the sliced ham evenly over the mayonnaise, followed by the slices of Swiss cheese, and finish with the remaining ham. Spread the honey mustard over the top layer of ham, then add the caramelized onions. Place the top half of the slider buns over the fillings. Using a brush, generously coat the tops of the buns with the poppy-butter mixture until well covered.

Slide the baking sheet into the preheated oven and bake for 10 to 12 minutes, or until the cheese has melted thoroughly and the tops of the buns are golden brown. Serve the sliders warm, straight from the oven, for a delightful treat.