Make the sauce by whisking the balsamic vinegar, honey, and soy sauce until well combined.
Prepare to cook the Brussels sprouts by heating the olive oil in a large cast-iron skillet over medium-high heat until it shimmers.
Cook the Brussels sprouts by adding the halved Brussels sprouts, cut-side down. Season with sea salt and freshly cracked black pepper to taste. Cook undisturbed for 5 to 7 minutes, until they are golden brown.
Add the garlic and cook, stirring constantly, for 1 minute.
Add the water and continue cooking, stirring occasionally, until the Brussels sprouts get slightly tender in the middle (they will finish cooking in the sauce), about 2-3 minutes.
Add the well-whisked sauce and cook, stirring constantly, for 1-2 minutes until the sauce reduces and thickens slightly.