Form the ground chuck into 1/3 pound balls, place on a plate, cover with plastic wrap, and refrigerate for 30 minutes.

Thinly slice white onions using a mandoline, place in a bowl, and squeeze out excess moisture. Refrigerate.

Cook bacon in a skillet over medium heat for 5-7 minutes until crispy, then chop and set aside.

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

Preheat a griddle over medium-high heat for 5 minutes. Add a drizzle of avocado oil.

Place burger balls on the hot griddle, smash with a spatula to form patties, and season with salt, pepper, and garlic powder.

After 3-4 minutes, add onions on top, flip burgers, and top with cheese. Cook for another 3 minutes until cheese melts.

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

Assemble the burgers with a generous layer of Baconnaise sauce, cheesy patty, more Baconnaise, and top bun. Press to secure.