Preheat oven to 350 degrees. Roll the crescent dough out onto an 11x17-inch pan, creating an even crust, and stretching to fit. Bake 7–8 minutes, or until browned. Allow to cool completely. Meanwhile, in a mixing bowl, combine the mayo, sour cream, cream cheese, and Ranch dressing mix. Spread filling over the top of the cooled crust. Combine the veggies and cheese, sprinkle over the filling. Cover with plastic wrap and refrigerate 3–4 hours. Cut into squares to serve.