BASE: Combine oats, brown sugar, flour and margarine; press onto bottom of 9-inch springform pan. Bake at 350, 15 minutes. BODY: Combine cream cheese, granulated sugar, peel and vanilla, mixing at medium speed on electric mixer until well blended. Add eggs, one at a time, mixing well after each addition; pour over crust. Bake at 325, 1 hour and 5 minutes. Loosen cake from rim of pan; cool before removing rim of pan. TOPPING: Combine brown sugar, corn syrup and margarine in saucepan; bring to boil, stirring constantly. Remove from heat; stir in vanilla. Chill until slightly thickened. Spoon over cheesecake. Garnish with orange slice and fresh mint, if desired.