Prepare the grill for direct cooking over medium heat (350° to 450°F) and preheat a Weber Gourmet BBQ System Griddle.
Cook the bacon on the griddle, with the lid closed, until it starts to soften, 3 to 4 minutes, stirring once or twice. Add the onions and cook, with the lid closed, until it starts to soften, 2 to 3 minutes, stirring occasionally. Add the brussels sprouts and garlic, season with salt and pepper, and cook, with the lid closed, until the brussels sprouts are crisp-tender and the garlic is lightly browned, 8 to 13 minutes, stirring occasionally. Add the vinegar during the last minute of cooking. Serve warm.
