Cut grapefruit in half. Carefully remove grapefruit segments with a paring knife, leaving shells intact. Remove and discard seeds and bitter pith from segments. Cut segments into bite-size pieces; place in a bowl. Peel tangerines with a paring knife, removing membranes between segments; cut segments into bite-size pieces, and add to bowl.
Add strawberries, kiwifruit, powdered sugar, and, if desired, orange flower water to bowl, stirring gently. Cover and chill 1 hour. Spoon mixture evenly into grapefruit shells; garnish, if desired.
*1/2 teaspoon grated orange rind may be substituted for 1 teaspoon orange flower water.
Note: Orange flower water can be found in some ethnic markets such as Asian, Mediterranean, or Italian.