Preheat oven to 425°F. Arrange cauliflower in a single layer on a rimmed baking sheet; brush both sides with olive oil. Sprinkle with a bit of salt and pepper.
Roast, turning once until cauliflower is tender and golden, about 35 minutes.
Remove from oven, and spoon spaghetti sauce over each piece of cauliflower. Sprinkle with mozzarella and half of the Parmesan cheese.
Broil cauliflower until cheese is bubbly and golden in spots, about 3 minutes.
Serve with remaining Parmesan cheese, and sprinkle with basil leaves.