Heat a griddle to 350ºF.
Combine the onion powder, garlic powder, pepper, and salt in a small bowl. Set aside.
Line a half sheet pan with parchment paper, and place the ground chuck in the middle of the pan. Cover the meat with a large sheet of plastic wrap and roll with a rolling pin (a wine bottle will do in a pinch) until the meat covers the surface of the pan; it should be very thin. Remove the plastic wrap and sprinkle the meat with the seasoning mixture. Fold the meat in half, widthwise, using the parchment paper. Roll a couple of times just to seal the two layers, then use a pizza wheel to cut the meat into 8 even squares.
Cook the burgers on the griddle for 2 to 3 minutes per side. Resist the urge to press them with your spatula. When cooked, stack them on one side of the griddle and cover with aluminum foil to keep warm.
Spread the onions out on the griddle and fry in the residual beef fat. Turn them every minute or so until they start to brown. Push over to the other side, opposite the patties.
Place the buns cut-side down on the griddle (don't worry, there will still be some fat there) and lay a sheet of foil over them for 2 minutes.
Construct the burgers thusly: Spread mayonnaise on the bottom bun. The fat will produce a moisture barrier, thus preventing said bun from becoming soggy. The cooked onion is next, followed by the meat. Stack pickles atop and finally the top bun, liberally mustarded. Repeat until there's nothing left to build. Consume.