You can make this without the pancetta or bacon substituting anchovy or leaving out all together. The apples add a caramelized sweetness. If you don't have brussels sprouts we often use wedges of cabbage in their place.
In a large frying pan render the pancetta by putting it in a cold pan and then raising the heat to medium allowing the fat to slowly cook out and crisp
Remove the pieces of meat leaving the fat in the pan
Add the brussels sprouts and apples with a big pinch of salt and several grinds of black pepper
Allow to caramelize, about 5 minutes, then stir to cook the other side
Remove from the heat and combine the cooked sprouts and apples with the crispy pancetta, mustard, olive oil, and pecans and serve immediately