Heat the water and the orange zest in a small saucepan; let steep for 3 minutes. Strain through fine-mesh sieve into a small bowl, reserving orange-flavored water. Discard zest.
Add gelatin to the flavored water, and let stand to soften, 2 minutes. Microwave 15 to 20 seconds to dissolve gelatin, or pour into small saucepan and dissolve over low heat.
Add orange juice concentrate and orange juice to gelatin mixture.
Beat egg substitute and sugar in bowl until light and thickened. Add gelatin mixture; stir to combine. Fold in yogurt until thoroughly combined. Divide chiffon evenly among six 2/3 cup custard cups or shaped molds. Freeze overnight, until set.
Combine raspberries, sugar and water in saucepan. Heat over medium heat until raspberries are softened, about 5 minutes. Strain through fine-mesh strainer over bowl, forcing mixture through with back of spoon or rubber spatula; discard seeds. Add more sugar to puree if too tart.
Run bottoms of cups under hot water until chiffons slide out easily. Unmold onto plate. Spoon sauce onto plates. Garnish with berries and mint if desired. Makes 6 servings.