Preheat oven to 425°F and line the baking tray with aluminum foil to make clean-up easier.
Drizzle sweet potatoes with 1/2 tablespoon of olive oil. Roast for 20 minutes or until tender. Remove from the oven and set aside.
Heat 1 tablespoon olive oil in a sauté pan over high heat and add brussels sprouts. Stir occasionally until caramelized.
Reduce the heat to medium low heat and add the onion. Cook slowly for 8 minutes and add the celery and continue cooking for another 6 minutes until onion is caramelized.
Increase heat to high and add sweet potatoes, grated apple and thyme. Season with salt and pepper and continue cooking for 3 to 4 minutes until heated thoroughly.
Serve hot immediately and enjoy!