1. Preheat oven to 400°. Bake oats in a 9-inch pie plate 10 to 12 minutes or until toasted and fragrant, stirring halfway through. Cool completely on a wire rack (about 30 minutes). Process oats in a blender or food processor 1 minute or until finely ground.
2. Beat butter and sugars at medium speed with a heavy-duty electric stand mixer until fluffy. Add eggs and vanilla, beating just until blended.
3. Stir together flour, next 3 ingredients, and ground oats in a small bowl; gradually add to butter mixture, beating just until blended after each addition. Fold in 2 1/4 cups chopped chocolate (about 2 bars) just until combined. Cover dough, and chill 8 to 12 hours.
4. Preheat oven to 350°. Drop dough by heaping tablespoonfuls onto parchment paper-lined baking sheets (about 6 per sheet).
5. Bake at 350° for 10 to 12 minutes or until golden brown; press remaining chocolate into cookies. Remove from baking sheets to wire racks; cool completely (about 15 minutes).