Preheat your oven to 375°F (190°C). Grease a 9x13-inch baking dish with olive oil.
In a large bowl, combine the spiralized or sliced sweet potatoes, onion, and garlic. Toss with olive oil, thyme, paprika, salt, and pepper until well coated.
Layer half of the sweet potato mixture in the prepared baking dish. Pour half of the heavy cream over the layer, then sprinkle with half of the cheddar cheese.
Add the remaining sweet potato mixture on top, pour the rest of the heavy cream, and finish with the remaining cheddar cheese.
Cover the baking dish with aluminum foil and bake for 30 minutes. Remove the foil and bake for an additional 15-20 minutes, or until the sweet potatoes are tender and the top is golden brown.
Allow to cool for 5 minutes before serving. Garnish with fresh parsley if desired.