Cut top 2 inches off sourdough loaf, reserving top; hollow out loaf, leaving a 1-inch-thick shell. (Reserve soft center of bread loaf for other uses, if desired.)
Drizzle 2 tablespoons vinaigrette evenly in bottom bread shell; layer with half of turkey, peppers, and cheese. Repeat layers, and top with bacon. Drizzle evenly with remaining 2 tablespoons vinaigrette, and cover with reserved bread top; press down firmly. Wrap in plastic wrap, and chill at least 1 hour or up to 8 hours before serving. Cut into 4 wedges. Garnish, if desired.
Note: For testing purposes only, we used Newman's Own Balsamic Vinaigrette salad dressing.