macOS not working on iMac after erasing HDD - showing Windows logo on startup
I have an iMac with Catalina. I use to have a partition splitting my 1TB HDD to have Windows using Bootcamp. After some use, I deleted the Windows partition thinking it was gone. Later I wanted to hard reset my iMac and erased data in the HD and HD - data disks. I then got a SMART error and tried to restart my iMac and found the windows logo coming on taking me to the windows error page.
I restarted and held command + R to get to Utilities. I got a spinning globe logo then the apple logo then reached Utilities, but not sure how to get macOS back again. See images on imgur for more.
This is unlikely to be a hardware problem since I have had no problems and this started literally after erasing data. Formatting possible? Any help is appreciated?