Combine beef and seasonings in a small bowl, and knead mixture by hand until integrated. Divide seasoned beef evenly into four balls. Flatten and form each ball into a square patty on a plate. Using a knife, make four small slits on the top of each patty. Place in the freezer for 5 minutes. Bring a pan sprayed with nonstick spray to medium-high heat on the stove. Spread onion out on the pan. Place the patties on top of the onion, slit-side down, and cover the pan. Cook for 3 to 4 minutes (no flipping necessary), or until cooked through. Meanwhile, cut each slice of bread into four squares, for a total of eight pieces. (If you like, slightly toast bread first.) Feel free to spread ketchup and/or mustard onto four pieces. Set aside. Once patties are cooked through, scoop each one along with the onion beneath it onto one piece of bread. Top each with a pickle chip and then another bread piece (or the other way around, if you want to be fancy!). Let them cool slightly, and then slide 'em into your mouth!