Grease a 9-inch (23-cm) flan tin with a removable bottom.
To make crumb crust, combine graham cracker crumbs, sugar, cinnamon and butter or margarine in a medium bowl.
Place crumb mixture in greased tin; press down slightly with the back of a spoon.
Refrigerate until firm.
To make filling and topping, blend cornstarch, sugar, vanilla and a little milk in a medium bowl.
Heat remaining milk in a medium saucepan; stir into cornstarch mixture.
Return to saucepan and bring to a boil, stirring constantly until thickened.
Cool, stirring occasionally to prevent a skin forming.
Drain gooseberries and reserve juice.
Drain peaches.
Spread cooled vanilla sauce over crumb crust; top with drained fruit as illustrated.
Prepare lemon-flavored gelatin using reserved gooseberry juice, according to package directions.
Cool slightly and pour over tart.
Refrigerate tart until firm then remove sides of flan tin and serve.