When summer nights call for a grilled burger, this one is our go-to. We season only the outside of each patty right before grilling to help a build a nice crust. Our trick for forming the patties is a real time saver, especially if you are cooking for a crowd. You can also form them the day before; place in an airtight container with parchment paper in between to help with party-day prep.
Form the ground beef into four 8-ounce patties. A quick and easy way to do this is to divide the meat into 4 piles. Place a pile on the top of a deli container lid. Take a second deli container lid and place the top of it against the meat. Press down evenly and firmly and watch as a perfect patty forms. Repeat with the remaining meat. Make an indentation in the middle of each patty with your thumb to keep the burger from shrinking as it cooks.
Sprinkle each patty on both sides with 3/4 teaspoon salt and 1/4 teaspoon pepper. Lightly brush the grill grates with oil. Grill the patties, indentation-side up, until marked on the bottom, about 4 minutes. Flip and cook until marked and slightly firm, about 4 more minutes for medium-rare. For cheeseburgers, top with 1 slice cheese during the last minute of cooking if desired; cover the grill to melt. Remove to a plate and let rest for 5 minutes.
While the burgers cook, place the onion slices on the grill (try to keep them together in a disk). Cook until they are golden on one side, about 4 minutes, then flip with a metal spatula and sprinkle generously with salt. Cook on the other side until the onions are lightly charred and softened through, about 4 minutes, and transfer to a plate.
Right before serving, toast the buns cut-side down on the grill. Top the bottom bun with a burger patty and layer with grilled onion, lettuce and a slice of tomato. Spread the inside of the top of each bun with some mayonnaise, mustard and ketchup. Arrange the pickle chips on top. Flip over to top the burgers and secure with a toothpick if desired.