Heat the olive oil in a large skillet over medium-high heat. Place the Brussels sprouts cut side down in a single layer, sprinkle with salt and pepper, and cook undisturbed for 4-5 minutes until deeply browned.

Flip the sprouts, add 2 tablespoons water, and cover. Cook for 2-3 minutes until fork-tender. Remove the lid, add the garlic, and cook for 30 seconds, stirring gently.

Remove from heat, drizzle with balsamic vinegar, and toss to coat, scraping up any browned bits. Serve immediately.