Preheat oven to 350 degrees F. In a medium bowl, whisk flour, cornstarch, baking powder, baking soda, and salt. In a large bowl, with mixer on medium speed, beat butter, brown sugar, and granulated sugar until creamy. Beat in eggs, 1 at a time. Beat in vanilla, followed by flour mixture. Fold in zucchini, chopped peanuts, and pretzels. By scant 1/3-cup scoopfuls, scoop dough onto 2 large cookie sheets, spacing about 1" apart. Bake 20 to 25 minutes or until bottoms are golden brown. Cool on sheets on wire racks.