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 become thoroughly hot.
03 - Divide ground beef into 8 equal portions and roll into balls. Season evenly with kosher salt and black pepper.
04 - Place beef balls on the hot skillet. Press each ball firmly with a spatula to create thin, smashed patties. Cook without disturbing for 2-3 minutes until deeply browned and crispy. Flip and cook 1-2 minutes longer. Remove from heat.
05 - Distribute mixed salad greens evenly among four serving bowls. Arrange cherry tomatoes, red onion, pickles, avocado, and shredded cheese on top of the greens.
06 - Place the cooked smashed burger patties over each assembled bowl, distributing them evenly among servings.
07 - Drizzle the prepared smash sauce generously over each bowl. Sprinkle with crispy fried onions if desired. Serve immediately while patties are still warm.