Crush the cookies in 2 batches in a food processor. You'll need about 4 1/3 cups crumbs.
Spread 1 1/3 cups crumbs over bottom of a 9-x-13-inch baking pan.
Cut away cardboard packaging from 1 carton of ice cream with scissors. Slice ice cream crosswise into 1-inch-thick rounds with a long knife. Arrange slices over crumbs, cutting smaller pieces to fill gaps. Cover ice cream with another 1 1/3 cups crumbs. Repeat with second container of ice cream, and top with remaining crumbs. Freeze until firm, at least 1 hour.
Mix frosting with enough green food coloring to make it bright green, then transfer to a pastry bag fitted with a plain tip. Arrange 3 double rows of pumpkins on top of cake and pipe vines connecting pumpkins. Freeze until ready to serve.
We loved Strange-1's "pumpkin patch" cake decorating idea! Her original recipe used a pudding-based layer; we adapted that part of the recipe so it uses just ice cream and crushed cookies, keeping it super simple.
Parchment can be used for easier cleanup/removal from the pan.