Thinly slice the yellow onion into half-moons.
Heat half of the olive oil in a skillet over medium-low heat; add the onions and a pinch of salt.
Cook the onions, stirring occasionally, until they are soft and golden brown, about 15 minutes.
While the onions are caramelizing, combine the ground beef with garlic powder, sea salt, and black pepper in a medium bowl.
Form the beef mixture into two equal-sized patties, pressing a small thumbprint into the center of each to prevent bulging.
Once the onions are finished, stir in the balsamic vinegar to deglaze the pan, then remove the onions and set them aside.
Wipe the skillet clean, add the remaining olive oil, and increase the heat to medium-high.
Place the beef patties in the skillet and sear for 4-5 minutes per side, or until they reach your desired level of doneness.
Plate the patties and top them generously with the warm caramelized onions before serving.