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!
PER SERVING (entire recipe, 4 sliders): 254 calories, 5.5gfat, 924mg sodium, 26g carbs, 6g fiber, 5.5g sugars, 29g protein