Preheat oven to 350 degrees F. Prepare a jelly roll pan with cooking spray; set aside.
To prepare crust, combine graham cracker crumbs, oil, and 3 tablespoons sugar. Pat crumb mixture evenly on bottom of prepared pan. Bake for 10 minutes; cool.
In a saucepan, combine gelatin and milk. Let stand 2 minutes. Then, heat over medium heat, stirring constantly, until gelatin is dissolved. Cool to room temperature; set aside.
In a mixing bowl, combine cream cheese, lemon juice, lemon peel, vanilla, and remaining sugar. Add milk mixture.
Pour entire mixture over baked crust.
Refrigerate until set, about 4 hours.
Decorate with berries in a flag design.