Something easier/faster than this? https://devzone.nordicsemi.com/b/blog/posts/getting-started-with-nordics-secure-dfu-bootloader
The procedure described in that link seems awfully laborious.
While the procedure described appears (and is) laborious, all except Step E are one-time setup stuff. Step E is the procedure to actually update an application OTA.
Secure DFU is quite complex, but as Richard D. you do not need all the steps every time. I do not think an even more condensed guide would be useful, as you need a minimum level of knowledge in order to understand the bootloader and DFU process. You might also want to refer to the bootloader documentation or DFU examples, but that will give you more information in a less condensed way (which I guess is not what you are looking for).