Place your jelly jars, lids, and rings in a large pot. Cover them with water and bring this to a boil on the stovetop. Allow them to continue to simmer while you work on the jam.
In a heavy-bottomed saucepot combine the strawberries, lemon zest, the juice of one lemon, and the sweetener. Sprinkle the xanthan gum over the top of this in a very thin and even layer. Stir to incorporate.
Bring the mixture to a boil over med-high and cover to help it reach a boil faster.
Once the mixture reaches a boil, uncover it, and reduce the heat to a simmer. Continue to stir occasionally to ensure the jam doesn't scald. Simmer for 30 minutes or until the desired consistency is reached.
Remove the hot jars and lids to a clean surface.
Fill the jars leaving a ½ to a ¼ of an inch of space at the top. Seal the jars immediately, and allow them to cool completely.
If you have sanitized your jars and lids in boiling water and used new discs, then you should be able to store your jam at room temperature. Once it is opened it should be kept in the fridge. Since this is such a small batch I store mine in the fridge once it is cooled, but if you make a larger batch follow the best practices for canning and jarring so that you can store it in dry storage!