Preheat oven to 350 degrees F. Grease bottom only of a 13 x 9 baking dish. Prepare brownie mix according to instructions on box. Sprinkle chopped pecans over top.
Bake brownies according to instructions. Let cool 10 minutes.
Melt caramels and water in saucepan over low heat, stirring frequently. Remove from heat and stir in vanilla. Drizzle caramel mixture over baked brownies in zigzag pattern. Place pecan halves on top of caramel. Let cool and serve with vanilla ice cream, if desired.