In a large bowl, toss the Brussels sprouts with 3 tablespoons olive oil and a generous sprinkle of salt and pepper.
Set a 12-inch skillet (preferably cast iron) over medium heat. Cook the bacon until crispy, about 5 minutes, then use a slotted spoon to transfer to a large bowl.
If there's not much bacon grease in the skillet, add 1 tablespoon of olive oil. Add the garlic and cook for about a minute until it is just starting to turn golden, then use a slotted spoon to transfer it to the bowl with the bacon.
Add the Brussels sprouts to the skillet. Try and make sure the cut sides are mostly down and keep them in as close to a single layer as possible; you'll probably have a little overlap. Cover skillet and cook for 5-6 minutes, until nearly tender.
Uncover and toss sprouts, then cook for a few minutes more until done to your liking. Stir in the bacon and garlic, then season to taste with salt and pepper. Serve immediately.