Heat oil in a large pan over medium-high heat. Add onion and saute until beginning to soften but not brown, 2 to 3 minutes. Stir in garlic and cook another minute. Add the cauliflower; salt and pepper to taste. Cook and stir another minute to combine.
Stir in the sauce and white wine; add 1 tablespoon of the parsley. Cook and stir 5 minutes at a low simmer.
Turn heat to medium-low, cover. Cook until cauliflower is almost tender, about 10 more minutes, stirring a few times.
Turn broiler to high. Line a rimmed baking sheet with foil. Spray lightly with cooking spray.
Pour cauliflower and tomato sauce onto the baking sheet. Gently scoop some of the tomato sauce back over the top of the cauliflower. Spread the cauliflower evenly on the sheet.
Sprinkle Parmesan cheese then mozzarella cheese over the cauliflower.
Broil until cheese is bubbly and slightly browned in spots, about 2 minutes. Watch carefully so cheese doesn't burn. Let rest 3 minutes before transferring to serving platter. Garnish with remaining fresh parsley.
