PREHEAT oven to 350°F. Mix ground beef, garlic powder, pepper and salt in medium bowl. Shape into large patty.
HEAT oil in large skillet on medium-high heat until shimmering. Add beef patty; cook 2 to 3 minutes on each side, or until seared. Using a spatula or wooden spoon, roughly chop the patty into pieces. Cook 3 to 4 minutes or until beef is cooked through. Drain fat and keep warm.
PLACE bottom halves of slider rolls in bottom of 13x9-inch baking dish. Top with cooked beef and layer with cheese slices. Top with Crispy Fried Onions. Spread cut side of tops of rolls with Mustard and place on top of Fried Onion layer.
BRUSH butter over tops of rolls and sprinkle with sesame seeds. Bake 15 to 20 minutes or until heated through and cheese is melted.