Preheat the broiler. Arrange the hamburger buns on a baking sheet. Brush the buns all over with 1T mayo. Toast until golden brown on both sides, 1-2 minutes. Cut into very small pieces and set aside.

Combine the cheese, 1/2C mayo and a pinch of salt in a food processor and process until smooth. Transfer to a bowl, cover and refrigerate until ready to use.

Whisk the remaining mayo, ketchup and mustard in a bowl for the sauce, cover and refrigerate until ready to use.

Arrange the bacon in a large nonstick skillet over medium-high heat. Add 1/3 of the onion and cook, stirring frequently, until soft, about 4 minutes. Add the beef, 3/4 tsp salt and some pepper. Cook, stirring and breaking up into small pieces, until browned, about 4 minutes. Stir in 1/3C of the prepared ketchup sauce and cool the beef mixture to room temperature.

Let the cheese mixture soften to room temperature, about 30 minutes before building dip. Layer the dip in a 3qt clear glass trifle or your favorite serving dish. Spread out the cheese mixture and then top, in even layers, with the buns, tomatoes, beef, remaining ketchup sauce, the pickles, the remaining onions and the bacon.

Wrap and refrigerate until chilled, about an hour. Top with the shredded lettuce right before serving. Serve with chips.