For the hash: Preheat a 12-inch cast iron skillet over medium heat. Render bacon slices in the skillet until almost crisp, about 7 to 10 minutes, then remove the bacon, chop small and set aside.
Pour off half the bacon fat from the skillet and add the sweet potatoes so they fill the bottom of the skillet. Increase the heat to medium-high and cook the potatoes for 3 to 5 minutes or until edges become brown. Turn them once with a spatula. Stir in the onions and cook another 5 minutes. Add the greens and wilt. When potatoes are fork tender, add chopped bacon and pecans. To caramelize, let sit 3 to 5 minutes, without turning, just before serving. Taste, and adjust seasoning with salt and pepper. Serve right away.