Use small cookie cutters to cut a pumpkin shape from each piece of American cheese and a ghost shape from each piece of mozzarella. Combine sirloin, Worcestershire sauce and salt in a medium bowl. Form into 8 small patties.
Warm oil in a large skillet over medium-high heat. Add patties and cook, turning once, until browned on each side, about 5 minutes total for medium. During last minute of cooking, place a mozzarella ghost or American cheese pumpkin on top of each slider.
Place a lettuce leaf and tomato slice on bottom half of each bun. Top with sliders, cheese side up. Serve with top halves of buns alongside sliders.