Preheat the oven to 425°F.
Coat all prepped veggies (sweet potato halves, onion quarters, and whole garlic cloves) with olive oil and salt, pepper, and spices to taste.
Place veggies on a baking tray with their cut sides are facing down, cover with aluminum foil, and put in the oven for 35 minutes.
After 35 minutes, check the doneness of the potatoes with a fork. If not soft enough, put back in the oven for another 5 minutes.