Add the basil leaves, sea salt and olive oil to a blender and process until smooth. Stir in the red pepper flakes and lemon juice.
Strain through a fine strainer for an extra smooth consistency If desired, but this is totally optional.
Drizzle over sliced tomatoes and mozzarella cheese. Can be store in the refrigerator for a few days, and remember to bring to room temperature for about half hour before serving.
Notes
Storage - best used right away, if need be it can be stored in the fridge for a couple of days but the color will darken and become brownish green. Alternatively it can be frozen in ice cube trays.