Choose the reddest rhubarb stalks you can find for this fool. Be sure to chill a mixing bowl before whipping the cream in it.
Tie cinnamon stick, cloves and lemon zest together in a cheesecloth bag. Combine rhubarb, sugar and spice bag in a large saucepan. Bring to a boil over medium-high heat. Cook, stirring occasionally, until mixture has consistency of applesauce, for 6 to 8 minutes. Discard spice bag. Chill rhubarb mixture for about 1 hour.
Meanwhile, line a colander with cheesecloth, and set it over a bowl. Spoon in yogurt, and let it drain in refrigerator until yogurt measures 11/2 cups, for 45 minutes to 1 hour.
Put drained yogurt in a bowl. Add rhubarb mixture, and fold lightly, leaving some swirls. Whip cream in a chilled bowl, and swirl it into fool. Spoon into individual dishes. Cover, and refrigerate for at least 1 hour or up to 6 hours.