To make the filling: Combine the sugar, lemon zest, eggs, flour, baking soda, salt and lemon juice in a medium-size bowl. Beat for 2 minutes. Pour over base. Return pan to microwave and cook at power 8 for 3 minutes until the filling is set but has a slight wiggle (like jello)Depending on the strength of your microwave it may need another minute. Cool completely. Refrigerate a minimum of 4 hours or overnight. Cut into squares and transport in a sealed plastic container. because the filling contains eggs, transport the squares n an ice-filled cooler as a precaution.