In large bowl toss prepared vegetables with bacon, 2 tablespoons of the oil, thyme, and 1/4 teaspoon each salt and pepper. Spread evenly in 15x10x1-inch baking pan. Place pan on lowest oven rack of cold oven; turn oven setting to 425 F. Roast 35 minutes, stirring vegetables every 10 minutes, until golden and tender.
Meanwhile, roll each piecrust to about 12 inches square. Cut each piecrust square in four free-form shapes; divide between two parchment-lined baking sheets.
Remove vegetables from oven; stir in 3/4 cup of the cheese, the vinegar, and garlic. Set aside. Leave oven on; adjust racks to lower center and upper positions.
Divide vegetable mixture among dough shapes, leaving generous 1-inch borders. Fold dough borders around vegetables, pleating as necessary to form tart edges. Sprinkle vegetables with remaining 1/4 cup goat cheese.
Bake 20 minutes or until tarts are golden brown, exchanging baking sheet placement on racks and rotating sheets after 10 minutes. Drizzle with remaining olive oil and garnish with rosemary sprigs. Makes 8 servings.