Combine the lemon zest and juice as well as the strawberries in a blender. Blend on high for 20 seconds or until smooth. Reduce the speed to low and remove the cover. Working slow and steady, pour in the sweetened condensed milk. Fold the strawberry mixture into the whipped cream using a rubber spatula. Pour into plastic container and place in the freezer for 2-3 hours. You can also place this into an ice cream maker.