01 - Whisk together mayonnaise, ketchup, yellow mustard, sweet pickle relish, white vinegar, smoked paprika, and black pepper in a small bowl until smooth and well combined. Set aside at room temperature.
02 - Place a large skillet or griddle over medium-high heat and allow it to become thoroughly hot, approximately 3–5 minutes. The surface should be smoking slightly for optimal searing.
03 - Divide the ground beef into 8 equal portions, rolling each into a loose ball. Season generously with kosher salt and freshly ground black pepper on all sides.
04 - Place beef balls onto the hot skillet. Using a heavy, flat spatula, press each ball down firmly until flattened into thin patties. Cook undisturbed for 2–3 minutes until deeply browned and crispy. Flip patties 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, sliced red onion, dill pickles, avocado, and shredded cheddar cheese over the greens in sections.
06 - Place two crispy smashed patties on top of each salad bowl, breaking them into bite-sized pieces if desired.
07 - Drizzle each bowl generously with the prepared smash sauce. Sprinkle crispy fried onions over the top if using. Serve immediately while patties are still warm.