Preheat oven to 350 degrees. Line a cookie sheet with parchment paper and set aside.
Finely chop white onion and scatter on parchment paper.
In a medium bowl, combine the ground beef and onion soup mix. Spread the mixture on top of the onions into a rectangular shape, a little larger than the Hawaiian rolls. Bake for 10 minutes. Remove from oven and let cool.
Without separating the slider rolls, cut them in half horizontally with a serrated knife. Place the bottom layer into a 9x13 baking dish.
Using two spatulas, transfer the meat to the baking dish, placing it on top of the bottom rolls. Top with cheese. Add pickles on top. Place top buns on burgers.
Melt 4 tablespoons of butter. Add in 1 teaspoon onion powder and mix well. Brush this on top of the buns.
Bake for 7-8 minutes, until the cheese is melted and the buns are slightly toasted.