Beef sliders are just the cutest little things to serve a crowd. And because of their cuteness, it seems they need gussying up with more than the traditional burger fare of mustard, ketchup and pickle or onion.These sliders here are topped with guacamole and a dollop of salsa, a grilled baby portabella mushroom and Swiss cheese, and grilled red onions and tangy horseradish mayonnaise.Grill sliders the same way you would a regular burger. Once cooked, top with desired toppings, or set out the toppings for your guests to create their own.You can use dinner rolls for sliders. They're just about the right size.Smaller sliders, about 1 1/2 inches in diameter, can be nestled them into mini pitas (about 3 inches in diameter). You can cut off one side of the pita and stuff the mini burger inside or cut the pita completely in half horizontally, making two pieces. You can serve these as appetizers.Beef Sliders Three WaysMakes 12. Prep time: 10 minutes. Total time: 40 minutes. You can make three varieties of sliders or make them all the same. Adjust the topping amounts to taste. The amounts for each topping are for 4 sliders. 12 beef sliders, 2 to 2 1/2 ounces each Salt and black pepper to taste 12 slider bunsFor Guacamole: 1/2 cup prepared guacamole 4 tablespoons salsa 4 tablespoons shredded Mexican cheese blendFor Mushroom:4 baby bella mushrooms, about 2 inches in diameter 1 tablespoon olive oil Salt and black pepper to taste 2 slices reduced-fat Swiss cheese Small torn pieces of lettuceFor Horseradish Mayo:1 small red onion, cut into 1/2-inch-thick slices Olive oil Salt and black pepper 1/3 cup reduced-fat mayonnaise 2 teaspoons prepared horseradish or to taste Small torn pieces of lettuceHEAT the grill to medium-high.ASSEMBLE all the slider ingredients. Set aside the guacamole and salsa. Wipe the mushrooms clean, brush with olive oil and sprinkle with salt and pepper. Grill the mushrooms until soft, about 3 minutes per side. Cut each Swiss cheese slice into quarters.BRUSH the red onion slices with oil and season with salt and pepper. Grill the onion slices at the same time you grill the mushrooms until they are tender.MIX the mayonnaise with the horseradish.SEASON sliders on each side with some salt and pepper. When the grill is hot, oil the grate.GRILL the sliders about 3 minutes on each side. Grill the slider buns if desired.REMOVE sliders from the grill.For the guacamole sliders: On the bottoms of four slider buns, spread some guacamole. Place a slider on top and top with some salsa and shredded Mexican cheese blend.For the mushroom sliders: Place some lettuce on the bottom bun and top with a slider. Add a quarter piece of Swiss cheese and top with a grilled mushroom.For the horseradish mayo sliders: Place some lettuce leaves on a bottom bun. Top with the grilled red onion and a slider. Place a dollop of the horseradish mayonnaise on the slider.