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 the ground beef into 8 equal portions and roll into balls. Season each ball generously with kosher salt and black pepper.
04 - Place beef balls onto the hot skillet. Press each ball down firmly with a heavy spatula to create thin, smashed patties. Cook undisturbed for 2-3 minutes until a deep brown crust forms. Flip and cook an additional 1-2 minutes until cooked through. Remove from heat.
05 - Distribute mixed salad greens evenly among four serving bowls. Arrange cherry tomatoes, sliced red onion, dill pickles, and sliced avocado over the greens.
06 - Place the cooked smash burger patties on top of each salad. Sprinkle shredded cheddar cheese over the patties while they're still warm.
07 - Drizzle the prepared smash sauce generously over each bowl. Top with crispy fried onions if desired. Serve immediately while patties are still warm.