I just made some lemon low fat frozen yoghurt from Jane Brody's recipe (Good Food Gourmet). It's totally simple.
3 cups low-fat (or part non and part low) yoghurt.
2 tsps vanilla extract (I use only 1 tsp)
4 tsps lemon zest
1/4 cup fresh squeezed lemon juice
1/2 cup sugar
Mix everything together and (as I do) freeze in a Donvier Ice Cream Maker or in freezer trays
If you use pans, she says to whip the mixture when it's partially frozen and then return to freezer to freeze solid.
Your mouth will pucker involuntarily, but it is really good and refreshing.