Thinly slice the yellow onion into half-moons.
Heat the avocado oil in a medium skillet over medium-low heat and add the onions, sea salt, and black pepper.
Cook the onions for 15 to 20 minutes, stirring occasionally, until they are deeply caramelized and golden brown.
While the onions cook, wrap one slice of bacon tightly around each beef hot dog in a spiral pattern.
Place the bacon-wrapped hot dogs in a separate skillet over medium heat, seam-side down first to seal the bacon.
Cook the hot dogs for 8 to 10 minutes, rotating frequently, until the bacon is crispy on all sides and the franks are heated through.
In a small bowl, whisk together the plain Greek yogurt and Dijon mustard until smooth to create a tangy protein-rich sauce.
Lay the butter lettuce leaves flat and place one bacon-wrapped hot dog in the center of each leaf.
Top each hot dog with a generous portion of caramelized onions and a drizzle of the mustard-yogurt sauce before serving.