Heat oven to 375° F. Wrap beets in a double layer of aluminum foil, seal and then bake until soft, about 75 min.
In a bowl, toss together carrots, squash, garlic, 2 tbsp olive oil, several thyme sprigs and ½ tsp each salt and pepper. Transfer to a rimmed baking sheet. Roast alongside the beets until just tender and golden, 35 to 40 min. Peel skin from cooked beets by rubbing with a paper towel, then cut beets into 1-inch pieces. Set aside.
Measure orange juice, then add enough vinegar to equal ⅔ cup. Whisk together juice, vinegar and ¼ tsp salt and drizzle in 2 tbsp olive oil, whisking constantly. Add thyme leaves and zest. Place vegetables on a serving dish and add orange vinaigrette. Garnish with thyme.
Food Styling Tip: As you'll see in the recipe, I've roasted the beets separately from the other vegetables. Not only do I really like roasting beets this way (wrapping in foil), it keeps them from "bleeding" or staining the other vegetables while cooking. The dish would not look quite as stunning on the plate if the beet juice had stained all of the other veggies. So you instantly become a talented food stylist by adding them just before serving!