Reinstall macOS on Ubuntu MBP After an update broke my 2015 MBP, I installed Ubuntu 18.04 on it (via USB). Now I want to go back to MacOS. When I boot into recovery mode (cmd+optn+R), I reach the usual menu of options. When I select the reinstall option, it takes me to the screen with the Mojave logo in a circle, and asks me which disk I want to install on.

However, no disks appear. Recovery mode doesn't seem to recognize that I have any hard drives at all

how can I reinstall MacOS on my laptop?
Instead of selecting the Reinstall option select the Disk Utility option at the bottom.

This will run Disk Utility and allow you to perform all of its usual functions, such as repairing your disk and formatting it.

Reading between the lines it's most likely you'll need to format the drive to make it available for the macOS installer. Once you've done this you can quit Disk Utility and you'll be returned to the previous menu to select the Reinstall option again.