Set a fine mesh stainless steel sieve over a bowl. Spoon in yogurt and let drain in the refrigerator until reduced to 1 cup, about 1 hour. Meanwhile, combine the blueberries, lemon juice, sugar and lemon zest in a saucepan. Stir over medium heat until the berries just begin to break down, 2 to 3 minutes. Transfer to a bowl and refrigerate. Just before serving, add the drained yogurt to the cooled berries and stir to combine. Makes 4 servings