Preheat oven to 350F. In 10-inch ovenproof skillet, heat the oil over med heat. (note: I cooked the bacon first, so I ended up cooking the onion in the bacon fat). Add the onion slices, 1/2 tsp of salt, and 1/8 tsp pepper. Cook, turning with tongs, until well browned, about 10 minutes. Sprinkle with the vinegar and cook 1 min. longer. Add the potatoes or rutabaga, greens, bacon(if using), and 1/2 tsp salt, and 1/8 tsp pepper. Pour the eggs over veg and stir to blend. Cook over med heat until the mixture begins to set, about 3 minutes. Place the skillet in the oven and bake for 15 min, or until set. Let stand 5 min, then invert onto a spatter. Cut into wedges, to serve.