How can I take of the problem?
I Have This Happening Yo My Plants Leaves What Is It and Is It Bad?
Certified GKH Gardening Expert
These are leaf galls and caused by pest activity.
Nasturtium actually act as a beneficial pest control by attracting pests to their leaves and flowers and saving other plants.
There is not management needed but you can spray with Neem Oil if you have a pest issue. Neem Oil is organic and safe for people, pets and bees.