Preheat the oven to 350 degrees F. Butter the bottom of a 13-by-9-inch baking dish.
Stir together the melted butter, poppy seeds, sesame seeds, dried garlic, dried onion and 1 teaspoon salt.
Without separating into individual rolls, slice the top half of the bread off the bottom. Place the bottom portion of the rolls in the prepared baking dish. Layer the shaved roast beef on top, then the crispy onions, then a layer of provolone, then top with layer of pickles. Place the top section of the rolls on the sandwich stacks. Stir the spiced butter and then liberally brush over the tops of the rolls until entirely coated.
Bake, uncovered, until the cheese is ooey gooey and the tops of the rolls are golden brown, 15 to 20 minutes. Cut into sliders with a large chef's knife.