You can download it here: https://apps.garmin.com/en-US/apps/a6d900b1-d0a7-4e33-af9c-6c45f3675018
Source code is also available: https://github.com/Shmuma/garmin-public/tree/master/pomodoro
Methodology details:
v0.1:
Basic functionality: track 25 minute work interval and 5 minutes rest interval, displays daily counts of such intervals.
Right now, I'm pretty satisfied with this app and use it daily. If you have extension ideas/feedback, please post it here.