1. Preheat the oven to 375 degrees F.
2. Mix together the sugar, applesauce and yogurt. When well-blended, add egg and vanilla and mix well.
3. Sift together the flour, baking powder and salt. Add to the wet ingredients and combine thoroughly. Gently fold in the blueberries and lemon zest.
4. Drop cookie dough onto baking sheets by tablespoons. Bake for 8-10 minutes, until the cookies are just brown at the edges. Cool on the baking sheet for two minutes and transfer to a wire rack to cool.