Preheat oven to 400 degrees
Put onions on a parchment lined baking sheet and drizzle with olive oil and water. Toss to coat and spread into an even layer.
Cut off top of garlic to expose cloves. Place garlic on a square of foil and drizzle with olive oil and season with salt and pepper. Bring corners of foil together to form a sealed package. Place on the baking sheet with the onions.
Place corn in the oven with onions and garlic. You can roast it in the husk or you can shuck it first and wrap it in foil
Roast onions, corn and garlic for 45 minutes, stirring the onions every 10 minutes
Turn oven down to 375 degrees
Spray sheet pan with cooking spray and unroll dough sheet onto pan. Prick dough all over with a fork and put in the oven for 5 minutes to partially set the crust
Squeeze garlic out of it's casing onto the partially baked crust and spread it out in an even layer
Spread Alfredo sauce on top in an even layer
Sprinkle with Mozzarella and chopped basil
Cut tomatoes in half and cut corn from the cobs
Put corn and tomatoes on top of Mozzarella and sprinkle with Parmesan
Bake for 10-14 minutes until hot and golden
Cut into large or small squares to serve