Preheat the grill to medium (400°F), or prepare a bed of hot coals in a campfire.
Place the beets on a large sheet of heavy-duty aluminum foil.
Drizzle with olive oil and season with salt and pepper, to taste.
Fold up the sides and ends of the foil to create a pouch.
Place the foil packet on the grill or over the hot coals and cook until the beets are tender, about 30 minutes.
Remove from the heat and carefully open the foil packet to let the steam escape. Let the beets cool for 5 minutes, then drizzle with the lemon thyme vinaigrette.
Transfer the beets to a bowl and top with goat cheese and mint, if using, just before serving. The salad can be served warm or at room temperature.
Notes
Hold the cheese--Add your goat cheese just before serving as the color of the beets will quickly stain the cheese.
Keep it simple--To keep dishes to a minimum, feel free to add the dressing and cheese directly to the foil packet after grilling and dig in.
Get ahead--The beets can be grilled up to 3 days before serving and the vinaigrette can be made up to 1 week before using.