Preheat oven to 400°. Trim and halve Brussels sprout ends and discard any discolored leaves (larger sprouts may need to be quartered to create even sized pieces).
Heat a large cast iron skillet over medium heat and fry diced bacon until crisp. Remove from skillet and drain on paper towel, set aside. The remaining pan drippings should equal about 1 tablespoon. In the skillet, toss sprouts in pan drippings to coat, sprinkle with salt and pepper, and place in the oven to roast for 20-30 minutes. Check and stir during cooking time. Sprouts should be fork tender and edges very crisp when done.
Removed from oven and toss with bacon and chopped pecans in skillet, return to oven for 5-10 minutes to warm bacon and crisp pecans. Transfer to a bowl and toss with balsamic to finish. Serve warm.