01 - Whisk together mayonnaise, ketchup, yellow mustard, sweet pickle relish, white vinegar, smoked paprika, and black pepper in a small bowl until smooth. Set aside to allow flavors to meld.
02 - Place a large skillet or griddle over medium-high heat and allow it to get thoroughly hot.
03 - Divide ground beef into 8 equal portions and form into balls. Season generously with kosher salt and freshly ground black pepper on all sides.
04 - Place beef balls onto the hot skillet. Press each ball down firmly with a heavy spatula to smash into thin patties. Cook undisturbed for 2-3 minutes until a dark crust forms. Flip and cook an additional 1-2 minutes for medium doneness. Remove from heat.
05 - Distribute mixed salad greens evenly among four serving bowls. Arrange cherry tomatoes, red onion, pickles, avocado, and shredded cheddar cheese on top of the greens.
06 - Place the cooked smashed burger patties over each bowl, distributing evenly among servings.
07 - Drizzle smash sauce generously over each bowl. Sprinkle with crispy fried onions if desired. Serve immediately while patties are still warm.