Cook onions in butter in large skillet on medium-high heat 15 to 20 min. or until onions are tender, stirring occasionally. Add dressing; cook on medium heat 10 min. or until onions are caramelized, stirring occasionally. Cool completely.
Heat oven to 450 degrees F. Press Perfect Parmesan Pizza Dough onto bottom of 15x10 1-inch pan sprayed with cooking spray. Let stand 10 min. Top with onions, cheese and tomatoes, Bake on bottom over rack 17 to 18 min. or until crust is golden brown.