Line two baking sheets with wax paper and spray lightly with cooking spray. Stir together the butter, maple syrup, and brown sugar in a medium saucepan. Bring the mixture to a boil over medium-high; boil, stirring constantly, for 3 minutes. Remove the pan from the heat, and stir in vanilla and salt. Let stand 3 minutes.
Process the toasted oats in a food processor until coarsely ground, about 20 to 30 seconds. Stir the oats and chopped pecans into the butter mixture. Drop the dough by rounded tablespoonfuls onto the prepared baking sheets and chill for 30 minutes. Before serving, press 1 pecan half onto each cookie. To store, layer the cookies between sheets of wax paper in an airtight container and refrigerate for up to 5 days.