Mix all campfire sauce ingredients in a small container. Refrigerate until serving.
Divide beef into 4 loose balls (~6 oz each). Mix dry seasonings in a small bowl.
Preheat cast iron skillet over campfire coals until very hot, 3–4 minutes.
Cook bacon in the dry skillet until crispy. Remove and set aside, leaving 1 tbsp bacon fat.
Place a beef ball in the skillet. Smash immediately with spatula, hold flat 10 seconds. Season top.
Cook 2–3 minutes until a deep crust forms. Flip. Add cheddar and a bacon strip on top.
Cook 1–2 more minutes until cheese is fully melted.
Toast buttered buns cut-side down on the skillet edge for 30–60 seconds.
Spread campfire sauce on both buns. Layer lettuce, patty, tomato, red onion, pickles. Serve immediately.