Allow cream cheese and eggs to stand at room temperature for 30 minutes. Meanwhile, preheat oven to 350 degrees F. For crust, in a food processor combine oats, pecans, 2 tablespoons brown sugar, and cinnamon. Cover and process with on/off pulses until oats and nuts are finely chopped. Add melted butter; cover and process with on/off pulses just until combined. Remove 1/4 cup of the oat mixture; set aside. Press the remaining oat mixture onto the bottom and about 1 inch up the sides of a 9-inch springform pan.
In a large mixing bowl beat cream cheese, granulated sugar, 1/2 cup brown sugar, flour, vanilla, and, if desired, orange peel with an electric mixer on medium speed until combined. Beat in milk until smooth. Stir in eggs and 1 cup of the butterscotch pieces.
Pour cream cheese mixture into crust-lined pan, spreading evenly. Sprinkle the reserved oat mixture and the remaining 1/4 cup butterscotch pieces around outside edge. Place springform pan in a shallow baking pan.
Bake for 45 to 50 minutes or until a 2 1/2-inch area around outside edge appears set when gently shaken. Cool in springform pan on a wire rack for 15 minutes. Using a small sharp knife, loosen crust from sides of pan. Cool for 30 minutes more. Remove sides of pan; cool cheesecake completely on wire rack. Cover and chill for at least 4 hours before serving.