Spread mayonnaise on the bottom half of each roll.
Layer each roll with a slice of turkey, bacon (broken in half or thirds to fit), a few diced pimientos or tomatoes, half a slice of Gruyere, and a sprinkling of Parmesan. Replace the tops. Repeat with the remaining rolls to assemble 12 sliders.
Arrange the sliders in a single layer in a greased 11x7-inch baking dish.
In a small saucepan over medium heat, melt the butter. Whisk in the brown sugar, Worcestershire sauce, garlic powder, and onion powder until the sugar is fully dissolved.
Pour or brush the butter sauce evenly over the sandwiches.
Cover with aluminum foil and refrigerate for at least 2 hours, or up to 8 hours.
Preheat the oven to 350°F. Bake covered for 25 minutes.
Remove the foil and bake uncovered for an additional 5 minutes, or until the tops are golden brown.