Cook the bacon over medium-high heat in a large skillet until crispy. A Dutch oven or a large cast iron pan works great. Set bacon on a plate and leave the drippings in the skillet.
Reduce to medium heat. Transfer cabbage and sliced onions to the skillet, stir well, and cover.
Cook with cover on. After about 5 minutes, the cabbage will begin to wilt.
Keep cooking, covered, stirring occasionally for 10 to 12 minutes. Remove the cover, sprinkle with sea salt and finish cooking the rest of the way, uncovered.