Cut bacon into half-inch strips. In a saute pan, render bacon halfway, then add Vidalia onion. Cook until onion is translucent and bacon is rendered.
Toss Brussels in vinegar, mustard, olive oil, salt and pepper. Place cut side down on a baking sheet and put in a 400 degree oven. Roast for 20-15 minutes.
Remove from oven. Combine roasted Brussels, onion, bacon and fresh thyme in a bowl and toss. Season with salt and pepper as needed. Serve.
