Prepare the burger balls by forming ground chuck into 1/3 pound balls. Refrigerate for 30 minutes.

Slice the white onions using a mandoline for uniformity and refrigerate to sharpen flavor.

Cook the bacon in a skillet until crispy, about 6-8 minutes. Drain and chop.

Combine mayo, ketchup, mustard, chopped bacon, Worcestershire sauce, apple cider vinegar, all-purpose rub, and red pepper flakes in a bowl to make baconnaise sauce. Refrigerate for 15 minutes.

Preheat the griddle over medium-high heat, then drizzle avocado oil to coat.

Cook the chilled burger balls on the hot griddle for 2-3 minutes without moving them.

Smash each ball into a flat patty and season with salt, pepper, and garlic. Cook for another 2-3 minutes.

Drizzle mustard on the patties and flip over, adding a slice of pepper jack cheese on each. Melt for 3 minutes.

Toast the burger buns on the griddle for 1-2 minutes until golden brown.

Assemble the burgers with a toasted bun, baconnaise sauce, cheesy patty, and more baconnaise sauce before topping with the other bun.