01 - Whisk together mayonnaise, ketchup, mustard, relish, 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 become thoroughly hot.
03 - Divide ground beef into 8 equal portions and roll into balls. Season generously with salt and pepper on all sides.
04 - Place beef balls onto the hot skillet. Press each ball firmly with a heavy spatula to smash into thin, wide patties. Cook undisturbed for 2-3 minutes until a deep brown crust forms. Flip and cook 1-2 minutes longer. Remove from skillet and set aside.
05 - Distribute mixed salad greens evenly among four large bowls. Arrange tomatoes, red onion, pickles, avocado, and shredded cheese over the greens.
06 - Place 2 cooked smash patties on top of each bowl.
07 - Drizzle smash sauce generously over each bowl. Sprinkle with crispy fried onions if desired. Serve immediately while patties are still warm.