Place a greased 9-in. springform pan on a double thickness of heavy-duty foil (about 18 in. square). Wrap foil securely around pan.
In a small bowl, mix the cracker crumbs, walnuts and sugar; stir in butter. Press onto bottom and 1 in. up sides of prepared pan. Place pan on a baking sheet. Bake at 325° for 10 minutes. Cool on a wire rack.
For filling, in a large bowl, beat cream cheese and sugar until smooth. Beat in the maple flavoring, extract and lemon zest. Add eggs; beat on low speed just until blended. Pour into crust. Place springform pan in a larger baking pan; add 1 in. of hot water to larger pan.
Bake for 45-55 minutes or until center is just set and top appears dull. Remove springform pan from water bath. Cool cheesecake on a wire rack for 10 minutes. Loosen sides from pan with a knife; remove foil. Cool 1 hour longer. Refrigerate overnight.
Remove rim from pan. If desired, drizzle cheesecake with melted chocolate.