In a medium bowl, stir together crushed graham crackers and melted margarine until combined. Press mixture onto bottom of a 9-inch springform pan. Cover and chill while preparing filling.
In a food processor, combine half of the ricotta cheese, half of the cream cheese, half of the pumpkin, and half of the milk. Cover and process or blend until smooth. Transfer to a large bowl. Repeat with remaining ricotta cheese, cream cheese, pumpkin, and milk.
In a small saucepan, sprinkle gelatin over orange juice; let stand for 5 minutes. Cook and stir over low heat until gelatin is dissolved. Stir into pumpkin mixture. Stir in orange peel, granulated sugar, brown sugar, vanilla, and 1 teaspoon pumpkin pie spice. Pour mixture into chilled crust. Cover and chill for at least 6 hours or until firm.
To serve, using a small sharp knife, loosen crust from side of springform pan; remove side of pan. Cut into wedges. If desired, garnish with whipped topping and sprinkle with additional pumpkin pie spice.