Assemble one slider by spreading mayonnaise on the bottom of the roll.
Add a layer of turkey, then bacon (breaking it in half or thirds to fit on the roll), a few diced pimientos (or tomatoes), half a slice of Gruyere, and a sprinkling of Parmesan cheese. Replace the top. Repeat with remaining rolls to assemble a total of 12 sandwiches.
Arrange sandwiches in a single layer in a greased 11 x 7-inch baking dish.
In a small skillet or saucepan, melt butter over medium heat. Whisk in the brown sugar, Worcestershire sauce, garlic powder, and onion powder. Continue whisking until the brown sugar is dissolved.
Pour the butter sauce 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 (180°C). Bake, covered, for 25 minutes.
Remove the foil and bake uncovered for an additional 5 minutes, or until golden brown.