You will have to open them up, remove the pit and then scoop the fleshy contents into a bowl. Use the fork to mash up the avocado into a puree and then add one teaspoon of lemon juice for each one. After you have mixed well, you can then stuff the mixture into ziplock bags. Try keep it to a maximum of two avocados per bag, in order to reduce the thawing time when you need to use them. Store in the freezer for 3 to 6 months, thaw for 24 hours in refrigerator before use.