Preheat oven to 425°.
Combine first 3 ingredients; set aside. Combine 1 cup milk and 2 tablespoons margarine in a large saucepan; bring to a boil. Reduce heat to low; add dry ingredients, stirring well until mixture is smooth and pulls away from sides of pan. Remove from heat; let cool 5 minutes.
Add egg whites and egg yolk, 1 at a time, beating at low speed of a mixer until smooth. Drop dough by level tablespoons, 2 inches apart, onto baking sheets coated with cooking spray. Bake at 425° for 10 minutes. Reduce oven temperature to 350°; bake an additional 10 minutes or until browned and crisp. Remove from oven; pierce the side of each cream puff with the tip of a sharp knife. Turn off oven; let cream puffs stand in partially closed oven for 5 minutes. Remove from baking sheet to a wire rack; let cool.
To prepare filling: Sprinkle gelatin over water in a small bowl; set aside. Combine 2 tablespoons sugar, cornstarch, and egg in a medium bowl. Stir with a whisk; set aside. Heat 3/4 cup milk over medium-high heat in a heavy saucepan to 180° or until tiny bubbles form around edge (do not boil). Gradually add hot milk to egg mixture; stirring constantly with a whisk. Return milk mixture to pan; add 1 1/2 teaspoons margarine. Bring to a boil over medium heat; cook 1 minute or until thick, stirring constantly with a whisk. Add soft gelatin to milk mixture; cook over low heat 1 minute, stirring until gelatin dissolves. Remove pan from heat; stir in cream of coconut, coconut extract, and vanilla. Place pan in a large ice-filled bowl; let stand 15 minutes or until room temperature (do not allow gelatin mixture to set). Remove pan from ice. Gently whisk in whipped topping. Cover and chill 4 hours or until thick.
Cut tops off cream puffs; fill each cream puff with 1 tablespoon filling. Sprinkle powdered sugar over cream puffs. Garnish with mint sprigs, if desired. Serve immediately.
Note: To make ahead, place baked and cooled cream puffs in a large heavy-duty zip-top plastic bag; seal. Freeze cream puffs. Cover and chill cooked filling. To reheat cream puffs, remove from bag and place on a large baking sheet. Bake at 325º for 10 minutes or until crisp. Remove from baking sheet to a wire rack; let cool completely. Fill according to recipe directions.