Trim the ends of the brussels sprouts, then peel and remove the tough outer leaves. Halve or quarter the sprouts. I halve the little ones and quarter the big ones. The goal is a roughly even width for all the sprouts so that they cook evenly.
Heat a cast iron skillet or other heavy bottomed pan over medium heat. Once hot, add the bacon pieces, stirring occasionally, and cook until brown and crispy, about 8 minutes. Add the cranberries and cook until warm and soft, about 1 minute. Remove the bacon and cranberries with a slotted spoon and set aside.
Increase heat to medium high. Add the avocado oil. Once hot and shimmering, add the brussels sprouts to the pan, toss to coat in the fat, and sauté, stirring occasionally, until golden brown and crispy, about 10 minutes.
Add the cooked bacon and cranberries back into the pan, then add the balsamic vinegar. Cook, stirring continuously, until the liquid evaporates, 2 minutes.
Remove from heat, season with salt and pepper to taste, and top with pistachios. Serve immediately.