Heat oven to 350ºF. In large bowl, break up cookie dough. Stir in pudding mix and milk until well blended. Stir or knead in 1/2 cup of the pistachios. Divide dough into 4 pieces. On ungreased large cookie sheet, press each piece into 6-inch round.
Bake 11 to 16 minutes or until edges are golden brown. Immediately cut each round into 8 wedges. Remove from cookie sheet; place on wire racks. Cool completely, about 30 minutes.
In 1-quart saucepan, heat vanilla chips and oil over low heat about 2 minutes, stirring constantly, until chips are melted and smooth. Drizzle over cooled wedges. Immediately sprinkle with remaining 1/4 cup pistachios; press in lightly.