Place the bacon slices in a cold skillet and turn the heat to medium, cooking until crispy, then remove and set aside on a paper towel.
Divide the ground beef into two equal-sized balls and season both sides generously with sea salt and black pepper.
Wipe the excess bacon grease from the skillet, add the avocado oil, and place the beef balls in the hot pan.
Immediately press the beef balls down with a heavy spatula to create thin, smashed patties and sear for 2-3 minutes until a deep crust forms.
Flip the patties, place the cheddar cheese on one patty to melt, and cook for another 2 minutes until fully cooked through.
Toast the sprouted grain bread slices in the same skillet until the edges are golden and crisp.
Assemble the melt by spreading Dijon mustard on one slice of bread, followed by the lettuce, tomato, red onion, both beef patties, and the crispy bacon.
Top with the second slice of bread and slice in half to serve.