Minimize handling of the meat and form it into four 4-ounce meatballs. Gently press each meatball to create a slightly flattened top.
Heat a small amount of neutral oil in a large cast-iron skillet over medium-high heat. Toast the cut sides of four burger buns for 1 to 2 minutes, then transfer them to plates or a platter.
Place half of the bacon in the skillet and cook until crisp, about 1 to 2 minutes per side. Transfer the bacon to two bottom buns.
Place two of the meatballs well apart in the skillet. Generously season each with salt and pepper.
Using a burger press, spatula, or the bottom of a 28-ounce can, flatten the meatballs as thin as possible. Top each with a handful of onions and jalapeños, pressing them into the meat. Cook undisturbed until browned, about 1.5 to 2 minutes.
Flip the patties and cook until the chicken is fully cooked, and the onions are golden, about 1 to 1.5 minutes.
Place the patties on the buns. Repeat with the remaining bacon, meat, onions, and jalapeños. There is no need to wipe out the pan before repeating.
