Preheat the oven to 425°F.

Remove the leaves from the cauliflower, and carefully cut off the bottom stem so that the cauliflower can sit on a flat surface.

In a small bowl, mix to combine the olive oil, garlic, thyme, and lemon juice.

Place the cauliflower on a baking sheet or in a cast iron skillet, and slowly pour the marinade over it. Rub it in as much as you can with your hands, and season generously with salt and pepper.

Roast for 1 to 1½ hours, or until the outside of the cauliflower is very roasted and brown.

Cut into wedges and serve.