Preheat oven to 400 degrees F. Cut tops off the beets and trim the root ends. Wash beets thoroughly. If using small beets, cut into 1- to 1-1/2-inch wedges. Place beets in a 3-quart rectangular baking dish. Add garlic and thyme sprigs. In a small bowl stir together 3 tablespoons of the olive oil, the salt, and pepper. Drizzle over vegetables in dish; toss lightly to coat. Cover dish with foil.
Roast for 40 to 45 minutes or until tender. (A knife should easily slide into the beets when they are tender.) Uncover and let beets cool in pan on a wire rack about 15 minutes. If using small beets, remove skins by wrapping the wedges, one at a time, in a paper towel and gently rubbing the skins off (use new paper towels as needed). (Baby beets do not need to be peeled.)
Remove garlic from the dish; finely chop garlic. Discard thyme sprigs. In a small bowl combine chopped garlic, the remaining 2 tablespoons olive oil, the lemon juice, and the 1 tablespoon snipped thyme. Drizzle oil mixture over beets; toss gently to coat.
Sprinkle beets with crumbled goat cheese, if desired, and additional snipped thyme. Serve warm or at room temperature.